diff --git a/lambda-test/command-test.c b/lambda-test/command-test.c
index 8474463..48fac5a 100644
--- a/lambda-test/command-test.c
+++ b/lambda-test/command-test.c
@@ -21,17 +21,17 @@
 
 static bool testIsSimulation(void) {
 	setupPorts();
-	setHeatingOn(false);
+	setHeaterOn(false);
 
 	assertFalse(isSimulation());
 	runCommand("se");
 	assertTrue(isSimulation());
 	assertTrue(getTime() == 0);
-	assertTrue(isHeatingOn());
+	assertTrue(isHeaterOn());
 	runCommand("sd");
 	assertFalse(isSimulation());
 	assertTrue(getTime() == 0);
-	// assertFalse(isHeatingOn());
+	// assertFalse(isHeaterOn());
 
 	return true;
 }
@@ -46,15 +46,15 @@
 	return true;
 }
 
-static bool testHeating(void) {
+static bool testHeater(void) {
 	setupPorts();
-	setHeatingOn(false);
+	setHeaterOn(false);
 
-	assertFalse(isHeatingOn());
+	assertFalse(isHeaterOn());
 	runCommand("he");
-	assertTrue(isHeatingOn());
+	assertTrue(isHeaterOn());
 	runCommand("hd");
-	assertFalse(isHeatingOn());
+	assertFalse(isHeaterOn());
 
 	return true;
 }
@@ -75,14 +75,14 @@
 /* Test names */
 static const char testIsSimulation_P[] PROGMEM = "testIsSimulation";
 static const char testIsLogging_P[] PROGMEM = "testIsLogging";
-static const char testHeating_P[] PROGMEM = "testHeating";
+static const char testHeater_P[] PROGMEM = "testHeater";
 static const char testCycleDisplay_P[] PROGMEM = "testCycleDisplay";
 
 /* Tests */
 static TestCase const tests[] = {
 		{class, testIsSimulation_P, testIsSimulation},
 		{class, testIsLogging_P, testIsLogging},
-		{class, testHeating_P, testHeating},
+		{class, testHeater_P, testHeater},
 		{class, testCycleDisplay_P, testCycleDisplay}
 };
 
diff --git a/lambda-test/display-test.c b/lambda-test/display-test.c
index 24fe5d2..1d62d72 100644
--- a/lambda-test/display-test.c
+++ b/lambda-test/display-test.c
@@ -27,32 +27,32 @@
 
 static bool testCycle(void) {
 	cancelAlert(true);
-	position = 0;
+	position = displayPosCurrent;;
 	updatePending = false;
 
-	assertTrue(position == 0);
+	assertTrue(position == displayPosCurrent);
 	assertFalse(updatePending);
 
 	cycleDisplay();
-	assertTrue(position == 1);
+	assertTrue(position == displayPosMax);
 	assertTrue(updatePending);
 	assertTrue(beepCount == 1);
 	assertTrue(beepLength == 2);
 
 	cycleDisplay();
-	assertTrue(position == 2);
+	assertTrue(position == displayPosHeater);
 	cycleDisplay();
-	assertTrue(position == 3);
+	assertTrue(position == displayPosLastText);
 	cycleDisplay();
-	assertTrue(position == 4);
+	assertTrue(position == displayPosTime);
 	cycleDisplay(); // roll over to 0
-	assertTrue(position == 0);
+	assertTrue(position == displayPosCurrent);
 
 	return true;
 }
 
 static bool testCycleCancelAlert(void) {
-	position = 0;
+	position = displayPosCurrent;;
 	updatePending = false;
 
 	alert(1, 1, 31, "", "", false);
@@ -60,7 +60,7 @@
 
 	cycleDisplay();
 	assertFalse(isAlertActive());
-	assertTrue(position == 0);
+	assertTrue(position == displayPosCurrent);
 	assertTrue(updatePending);
 
 	return true;
diff --git a/lambda-test/interrupts-test.c b/lambda-test/interrupts-test.c
index 8e7902e..76c54c3 100644
--- a/lambda-test/interrupts-test.c
+++ b/lambda-test/interrupts-test.c
@@ -24,7 +24,7 @@
 	// test that the beep output pin is enabled
 	assertTrue(bit_is_set(DDRB, PB1));
 
-	// test that the oxygen sensor heating control output pin is enabled
+	// test that the oxygen sensor heater control output pin is enabled
 	assertTrue(bit_is_set(DDRB, PB1));
 
 	return true;
diff --git a/lambda-test/rules-test.c b/lambda-test/rules-test.c
index b9880ea..147660d 100644
--- a/lambda-test/rules-test.c
+++ b/lambda-test/rules-test.c
@@ -25,34 +25,34 @@
 	Measurement meas = {0, 0, 0};
 
 	resetRules();
-	dir = -1;
+	dir = burning_down;
 	reason(meas);
 	assertFalse(rules[0].fired);
 
 	resetRules();
-	dir = 0;
+	dir = none;
 	reason(meas);
 	assertFalse(rules[0].fired);
 
 	resetRules();
-	dir = 1;
+	dir = firing_up;
 	reason(meas);
 	assertFalse(rules[0].fired);
 
 	meas.tempI = 500;
 
 	resetRules();
-	dir = -1;
+	dir = burning_down;
 	reason(meas);
 	assertFalse(rules[0].fired);
 
 	resetRules();
-	dir = 0;
+	dir = none;
 	reason(meas);
 	assertFalse(rules[0].fired);
 
 	resetRules();
-	dir = 1;
+	dir = firing_up;
 	reason(meas);
 	assertTrue(rules[0].fired);
 	assertTrue(50 == airgate);
@@ -67,34 +67,34 @@
 	Measurement meas = {999, 0, 0};
 
 	resetRules();
-	dir = 1;
+	dir = firing_up;
 	reason(meas);
 	assertFalse(rules[1].fired);
 
 	resetRules();
-	dir = 0;
+	dir = none;
 	reason(meas);
 	assertFalse(rules[1].fired);
 
 	resetRules();
-	dir = -1;
+	dir = burning_down;
 	reason(meas);
 	assertFalse(rules[1].fired);
 
 	meas.tempI = 799;
 
 	resetRules();
-	dir = 1;
+	dir = firing_up;
 	reason(meas);
 	assertFalse(rules[1].fired);
 
 	resetRules();
-	dir = 0;
+	dir = none;
 	reason(meas);
 	assertFalse(rules[1].fired);
 
 	resetRules();
-	dir = -1;
+	dir = burning_down;
 	reason(meas);
 	assertTrue(rules[1].fired);
 	assertTrue(25 == airgate);
@@ -109,34 +109,34 @@
 	Measurement meas = {999, 0, 0};
 
 	resetRules();
-	dir = 1;
+	dir = firing_up;
 	reason(meas);
 	assertFalse(rules[2].fired);
 
 	resetRules();
-	dir = 0;
+	dir = none;
 	reason(meas);
 	assertFalse(rules[2].fired);
 
 	resetRules();
-	dir = -1;
+	dir = burning_down;
 	reason(meas);
 	assertFalse(rules[2].fired);
 
 	meas.tempI = 399;
 
 	resetRules();
-	dir = 1;
+	dir = firing_up;
 	reason(meas);
 	assertFalse(rules[2].fired);
 
 	resetRules();
-	dir = 0;
+	dir = none;
 	reason(meas);
 	assertFalse(rules[2].fired);
 
 	resetRules();
-	dir = -1;
+	dir = burning_down;
 	reason(meas);
 	assertTrue(rules[2].fired);
 	assertTrue(0 == airgate);
@@ -149,9 +149,9 @@
 static bool testTooRich(void) {
 
 	Measurement meas = {0, 0, 0};
-	dir = 0;
+	dir = none;
 
-	setHeatingState(HEATING_READY);
+	setHeaterState(heaterStateReady);
 
 	meas.tempI = 100;
 	meas.lambda = 2000;
@@ -200,9 +200,9 @@
 static bool testTooLean(void) {
 
 	Measurement meas = {0, 0, 0};
-	dir = 0;
+	dir = none;
 
-	setHeatingState(HEATING_READY);
+	setHeaterState(heaterStateReady);
 
 	meas.tempI = 500;
 	meas.lambda = 1601;
@@ -246,7 +246,7 @@
 
 	resetRules();
 	Measurement meas = {0, 0, 0};
-	dir = 1;
+	dir = firing_up;
 
 	meas.tempI = 50;
 	age = 0;
@@ -278,96 +278,96 @@
 	return true;
 }
 
-static bool testHeatingReady(void) {
+static bool testHeaterReady(void) {
 
 	resetRules();
 	resetTime();
 	Measurement meas = {0, 0, 0};
-	dir = 1;
+	dir = firing_up;
 
-	setHeatingOn(false);
+	setHeaterOn(false);
 	meas.current = 1300;
 	reason(meas);
-	assertTrue(HEATING_OFF == getHeatingState());
+	assertTrue(heaterStateOff == getHeaterState());
 
-	setHeatingOn(true);
+	setHeaterOn(true);
 	meas.current = 5000;
 	reason(meas);
-	assertTrue(HEATING_UP == getHeatingState());
+	assertTrue(heaterStateUp == getHeaterState());
 
-	setHeatingOn(true);
+	setHeaterOn(true);
 	meas.current = 1300;
 	reason(meas);
-	assertTrue(HEATING_READY == getHeatingState());
+	assertTrue(heaterStateReady == getHeaterState());
 
 	cancelAlert(false);
 
 	return true;
 }
 
-static bool testHeatingFaultNoconn(void) {
+static bool testHeaterFaultNoconn(void) {
 
 	resetRules();
 	resetTime();
 	Measurement meas = {0, 0, 0};
-	dir = 1;
+	dir = firing_up;
 
-	setHeatingOn(true);
+	setHeaterOn(true);
 	meas.current = 0;
 	reason(meas);
-	assertTrue(HEATING_FAULT == getHeatingState());
+	assertTrue(heaterStateFault == getHeaterState());
 
 	cancelAlert(false);
 
 	return true;
 }
 
-static bool testHeatingFaultShort(void) {
+static bool testHeaterFaultShort(void) {
 
 	resetRules();
 	resetTime();
 	Measurement meas = {0, 0, 0};
-	dir = 1;
+	dir = firing_up;
 
-	setHeatingOn(true);
+	setHeaterOn(true);
 	meas.current = 8000;
 	reason(meas);
-	assertTrue(HEATING_FAULT == getHeatingState());
+	assertTrue(heaterStateFault == getHeaterState());
 
 	cancelAlert(false);
 
 	return true;
 }
 
-static bool testHeatingFaultNoheat(void) {
+static bool testHeaterFaultNoheat(void) {
 
 	resetRules();
 	resetTime();
 	Measurement meas = {0, 0, 0};
-	dir = 1;
+	dir = firing_up;
 
-	setHeatingOn(true);
+	setHeaterOn(true);
 
 	// more than 3 mins
 	addInts(INTS_PER_SEC * 181);
 
 	meas.current = 5000;
 	reason(meas);
-	assertTrue(HEATING_FAULT == getHeatingState());
+	assertTrue(heaterStateFault == getHeaterState());
 
 	cancelAlert(false);
 
 	return true;
 }
 
-static bool testHeatingTimeout(void) {
+static bool testHeaterTimeout(void) {
 
 	resetRules();
 	resetTime();
 	Measurement meas = {0, 0, 0};
-	dir = 1;
+	dir = firing_up;
 
-	setHeatingOn(true);
+	setHeaterOn(true);
 
 	// more than 3 hours below 400°C
 	addInts(INTS_PER_SEC * 10800UL);
@@ -375,7 +375,7 @@
 	meas.tempI = 300;
 	meas.current = 1300;
 	reason(meas);
-	assertTrue(HEATING_OFF == getHeatingState());
+	assertTrue(heaterStateOff == getHeaterState());
 
 	cancelAlert(false);
 
@@ -498,11 +498,11 @@
 static const char testTooRich_P[] PROGMEM = "testTooRich";
 static const char testTooLean_P[] PROGMEM = "testTooLean";
 static const char testFireOut_P[] PROGMEM = "testFireOut";
-static const char testHeatingReady_P[] PROGMEM = "testHeatingReady";
-static const char testHeatingFaultNoconn_P[] PROGMEM = "testHeatingFaultNoconn";
-static const char testHeatingFaultShort_P[] PROGMEM = "testHeatingFaultShort";
-static const char testHeatingFaultNoheat_P[] PROGMEM = "testHeatingFaultNoheat";
-static const char testHeatingTimeout_P[] PROGMEM = "testHeatingTimeout";
+static const char testHeaterReady_P[] PROGMEM = "testHeaterReady";
+static const char testHeaterFaultNoconn_P[] PROGMEM = "testHeaterFaultNoconn";
+static const char testHeaterFaultShort_P[] PROGMEM = "testHeaterFaultShort";
+static const char testHeaterFaultNoheat_P[] PROGMEM = "testHeaterFaultNoheat";
+static const char testHeaterTimeout_P[] PROGMEM = "testHeaterTimeout";
 static const char testReasonDirBurnUp_P[] PROGMEM = "testReasonDirBurnUp";
 static const char testReasonDirBurnDown_P[] PROGMEM = "testReasonDirBurnDown";
 
@@ -514,11 +514,11 @@
 		{class, testTooRich_P, testTooRich},
 		{class, testTooLean_P, testTooLean},
 		{class, testFireOut_P, testFireOut},
-		{class, testHeatingReady_P, testHeatingReady},
-		{class, testHeatingFaultNoconn_P, testHeatingFaultNoconn},
-		{class, testHeatingFaultShort_P, testHeatingFaultShort},
-		{class, testHeatingFaultNoheat_P, testHeatingFaultNoheat},
-		{class, testHeatingTimeout_P, testHeatingTimeout},
+		{class, testHeaterReady_P, testHeaterReady},
+		{class, testHeaterFaultNoconn_P, testHeaterFaultNoconn},
+		{class, testHeaterFaultShort_P, testHeaterFaultShort},
+		{class, testHeaterFaultNoheat_P, testHeaterFaultNoheat},
+		{class, testHeaterTimeout_P, testHeaterTimeout},
 		{class, testReasonDirBurnUp_P, testReasonDirBurnUp},
 		{class, testReasonDirBurnDown_P, testReasonDirBurnDown}
 };
diff --git a/lambda-test/sensors-test.c b/lambda-test/sensors-test.c
index 95679e1..e8e55f8 100644
--- a/lambda-test/sensors-test.c
+++ b/lambda-test/sensors-test.c
@@ -34,9 +34,9 @@
 	// enable pull-up resistor so the measured voltage
 	// should be close to AREF
 	PORTC |= ((1 << ADC_TEMPI) | (1 << ADC_TEMPO) | (1 << ADC_LAMBDA) |
-			(1 << ADC_HEATING));
+			(1 << ADC_HEATER));
 
-	setHeatingState(HEATING_READY);
+	setHeaterState(heaterStateReady);
 
 	// do many measurements so the averaged voltages are near the measured
 	// voltages (close to AREF)
@@ -185,25 +185,25 @@
 	return ! strcmp(info, MSG_RICH);
 }
 
-static bool testSetHeatingOn(void) {
-	setHeatingOn(true);
-	assertTrue(isHeatingOn());
-	assertTrue(HEATING_UP == getHeatingState());
+static bool testSetHeaterOn(void) {
+	setHeaterOn(true);
+	assertTrue(isHeaterOn());
+	assertTrue(heaterStateUp == getHeaterState());
 
-	setHeatingOn(false);
-	assertFalse(isHeatingOn());
-	assertTrue(HEATING_OFF == getHeatingState());
+	setHeaterOn(false);
+	assertFalse(isHeaterOn());
+	assertTrue(heaterStateOff == getHeaterState());
 
 	return true;
 }
 
-static bool testSetHeatingState(void) {
-	setHeatingOn(false);
-	assertFalse(isHeatingOn());
-	assertTrue(HEATING_OFF == getHeatingState());
+static bool testSetHeaterState(void) {
+	setHeaterOn(false);
+	assertFalse(isHeaterOn());
+	assertTrue(heaterStateOff == getHeaterState());
 
-	setHeatingState(HEATING_FAULT);
-	assertTrue(HEATING_FAULT == getHeatingState());
+	setHeaterState(heaterStateFault);
+	assertTrue(heaterStateFault == getHeaterState());
 
 	return true;
 }
@@ -232,8 +232,8 @@
 static const char testToInfoOkay_P[] PROGMEM = "testToInfoOkay";
 static const char testToInfoIdeal_P[] PROGMEM = "testToInfoIdeal";
 static const char testToInfoRich_P[] PROGMEM = "testToInfoRich";
-static const char testSetHeatingOn_P[] PROGMEM = "testSetHeatingOn";
-static const char testSetHeatingState_P[] PROGMEM = "testSetHeatingState";
+static const char testSetHeaterOn_P[] PROGMEM = "testSetHeaterOn";
+static const char testSetHeaterState_P[] PROGMEM = "testSetHeaterState";
 
 /* Tests */
 static TestCase const tests[] = {
@@ -257,8 +257,8 @@
 		{class, testToInfoOkay_P, testToInfoOkay},
 		{class, testToInfoIdeal_P, testToInfoIdeal},
 		{class, testToInfoRich_P, testToInfoRich},
-		{class, testSetHeatingOn_P, testSetHeatingOn},
-		{class, testSetHeatingState_P, testSetHeatingState}
+		{class, testSetHeaterOn_P, testSetHeaterOn},
+		{class, testSetHeaterState_P, testSetHeaterState}
 };
 
 TestClass sensorsClass = {tests, sizeof(tests) / sizeof(tests[0])};
diff --git a/lambda/TODO b/lambda/TODO
index ea873a1..9594df8 100644
--- a/lambda/TODO
+++ b/lambda/TODO
@@ -6,7 +6,6 @@
 - Take in account F_CPU everywhere CPU speed matters
 
 * Functionality
-- Show fire dir and (recommended) airgate position?
   
 * Circuit
 - AVCC should be connected to VCC via an LC network
@@ -16,4 +15,4 @@
 - pins.h LCD pins
 - interrupts.h: INTS_PER_SEC 61
 - sensors.h: SHUNT_MILLIOHMS 100
-- rules.c: heatingTimeout(): getTime() >= 10800
\ No newline at end of file
+- rules.c: heaterTimeout(): getTime() >= 10800
\ No newline at end of file
diff --git a/lambda/command.c b/lambda/command.c
index 14b8216..bc2eab3 100644
--- a/lambda/command.c
+++ b/lambda/command.c
@@ -43,7 +43,7 @@
 		resetTime();
 		resetDisplay();
 		resetRules();
-		setHeatingOn(true);
+		setHeaterOn(true);
 		beep(1, 2, 31);
 	}
 	else if (strcmp_P(fields[0], PSTR("sd")) == 0) {
@@ -65,13 +65,13 @@
 		beep(1, 2, 31);
 	}
 	else if (strcmp_P(fields[0], PSTR("he")) == 0) {
-		// oxygen sensor heating enable
-		setHeatingOn(true);
+		// oxygen sensor heater enable
+		setHeaterOn(true);
 		beep(1, 2, 31);
 	}
 	else if (strcmp_P(fields[0], PSTR("hd")) == 0) {
-		// oxygen sensor heating disable
-		setHeatingOn(false);
+		// oxygen sensor heater disable
+		setHeaterOn(false);
 		beep(1, 2, 31);
 	}
 	else if (strcmp_P(fields[0], PSTR("cm")) == 0) {
@@ -101,8 +101,8 @@
 		// assuming one measurement was logged per second
 		addInts(INTS_PER_SEC);
 		Measurement meas = readMeas(fields, fieldCount);
-		if (getHeatingState() == HEATING_OFF ||
-				getHeatingState() == HEATING_READY) {
+		if (getHeaterState() == heaterStateOff ||
+				getHeaterState() == heaterStateReady) {
 			updateMeas(meas);
 		}
 		reason(meas);
diff --git a/lambda/display.c b/lambda/display.c
index b31bf76..b932ad2 100644
--- a/lambda/display.c
+++ b/lambda/display.c
@@ -23,13 +23,7 @@
 #include "messages.h"
 #include "rules.h"
 
-#define MENU_OFF 0
-#define MENU_MAX_VALUES 1
-#define MENU_CURRENT 2
-#define MENU_LAST_TEXT 3
-#define MENU_TIME 4
-
-uint8_t position = MENU_OFF;
+DisplayPos position = displayPosCurrent;
 bool updatePending = false;
 Measurement measLatest = {0, 0, 2000, 0};
 Measurement measMax = {0, 0, 2000, 0};
@@ -63,7 +57,7 @@
 	char line0[17];
 	char line1[17];
 	snprintf(line0, sizeof(line0), "Ti %3dC To %3dC ", meas.tempI, meas.tempO);
-	if (getHeatingState() == HEATING_READY || position == MENU_MAX_VALUES) {
+	if (getHeaterState() == heaterStateReady || position == displayPosMax) {
 		snprintf(line1, sizeof(line1), "L  %d.%02d %s %s",
 				lambdaT.quot, abs(lambdaT.rem), toInfo(lambdax100), hint);
 	} else {
@@ -81,7 +75,7 @@
 
 	char line1[17];
 	snprintf(line1, sizeof(line1), "%d.%02d Amp", ampsT.quot, abs(ampsT.rem));
-	setText(MSG_HEATING_CURRENT, line1);
+	setText(MSG_HEATER_CURRENT, line1);
 }
 
 /**
@@ -101,8 +95,8 @@
 		return;
 	}
 	position++;
-	if (position > MENU_TIME) {
-		position = MENU_OFF;
+	if (position > displayPosTime) {
+		position = displayPosCurrent;
 	}
 	updatePending = true;
 	beep(1, 2, 31);
@@ -130,19 +124,19 @@
 	if (updatePending && ! isAlertActive()) {
 		updatePending = false;
 
-		if (position == MENU_MAX_VALUES) {
+		if (position == displayPosMax) {
 			displayMeas(measMax, " ^");
-		} else if (position == MENU_LAST_TEXT) {
+		} else if (position == displayPosLastText) {
 			setText(lastLine0, lastLine1);
-		} else if (position == MENU_CURRENT) {
+		} else if (position == displayPosHeater) {
 			displayCurrent(measLatest.current);
-		} else if (position == MENU_TIME) {
+		} else if (position == displayPosTime) {
 			displayTime();
 		} else {
 			char* hint;
 			switch (getDir()) {
-				case DIR_BURN_UP: hint = " >"; break;
-				case DIR_BURN_DOWN: hint = " <"; break;
+				case firing_up: hint = " >"; break;
+				case burning_down: hint = " <"; break;
 				default: hint = " -"; break;
 			}
 			displayMeas(measLatest, hint);
diff --git a/lambda/display.h b/lambda/display.h
index 0d1ff09..efaf506 100644
--- a/lambda/display.h
+++ b/lambda/display.h
@@ -13,6 +13,17 @@
 
 #include "sensors.h"
 
+/**
+ * Display positions.
+ */
+typedef enum {
+	displayPosCurrent = 0,
+	displayPosMax = 1,
+	displayPosHeater = 2,
+	displayPosLastText = 3,
+	displayPosTime = 4
+} DisplayPos;
+
 uint8_t getPosition(void);
 
 /**
diff --git a/lambda/lambda.c b/lambda/lambda.c
index 70b6768..2b38ce3 100644
--- a/lambda/lambda.c
+++ b/lambda/lambda.c
@@ -23,6 +23,7 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <avr/pgmspace.h>
+#include <avr/power.h>
 #include "usart.h"
 #include "lcdroutines.h"
 #include "adc.h"
@@ -39,6 +40,9 @@
  * runs commands sent via USART.
  */
 int main(void) {
+
+	// clock_prescale_set(clock_div_1);
+
 	initUSART();
 	lcd_init();
 	setupPorts();
@@ -50,7 +54,7 @@
 	alert_P(1, 2, 31, PSTR(MSG_WELCOME), PSTR(""), false);
 	// spend some time on being polite
 	while (getTime() < 3) {}
-	setHeatingOn(true);
+	setHeaterOn(true);
 
 	uint32_t ints = 0;
 	Measurement meas;
diff --git a/lambda/messages.h b/lambda/messages.h
index fcd2cd8..7c16f89 100644
--- a/lambda/messages.h
+++ b/lambda/messages.h
@@ -30,15 +30,15 @@
 	#define MSG_TOO_RICH_0 "Too rich, open"
 	#define MSG_TOO_RICH_1 "air gate"
 	#define MSG_FIRE_OUT_0 "Fire out?"
-	#define MSG_HEATING_UP_0 "Oxygen sensor"
-	#define MSG_HEATING_UP_1 "heating up..."
-	#define MSG_HEATING_READY_0 "Oxygen sensor"
-	#define MSG_HEATING_READY_1 "ready"
-	#define MSG_HEATING_FAULT_0 "Oxygen sensor"
-	#define MSG_HEATING_FAULT_1 "heating fault!"
-	#define MSG_HEATING_OFF_0 "Oxygen sensor"
-	#define MSG_HEATING_OFF_1 "off"
-	#define MSG_HEATING_CURRENT "Heater current"
+	#define MSG_HEATER_UP_0 "Oxygen sensor"
+	#define MSG_HEATER_UP_1 "heating up..."
+	#define MSG_HEATER_READY_0 "Oxygen sensor"
+	#define MSG_HEATER_READY_1 "ready"
+	#define MSG_HEATER_FAULT_0 "Oxygen sensor"
+	#define MSG_HEATER_FAULT_1 "heater fault!"
+	#define MSG_HEATER_OFF_0 "Oxygen sensor"
+	#define MSG_HEATER_OFF_1 "off"
+	#define MSG_HEATER_CURRENT "Heater current"
 	#define MSG_TIME_SINCE_START "Time since start"
 
 #elif LANG == 1
@@ -59,15 +59,15 @@
 	#define MSG_TOO_RICH_0 "Zu fett, Luft-"
 	#define MSG_TOO_RICH_1 "schieber oeffnen"
 	#define MSG_FIRE_OUT_0 "Feuer aus?"
-	#define MSG_HEATING_UP_0 "Lambdasonde"
-	#define MSG_HEATING_UP_1 "waermt auf..."
-	#define MSG_HEATING_READY_0 "Lambdasonde"
-	#define MSG_HEATING_READY_1 "bereit"
-	#define MSG_HEATING_FAULT_0 "Lambdasonden-"
-	#define MSG_HEATING_FAULT_1 "heizung Fehler!"
-	#define MSG_HEATING_OFF_0 "Lambdasonde"
-	#define MSG_HEATING_OFF_1 "aus"
-	#define MSG_HEATING_CURRENT "Heizstrom"
+	#define MSG_HEATER_UP_0 "Lambdasonde"
+	#define MSG_HEATER_UP_1 "waermt auf..."
+	#define MSG_HEATER_READY_0 "Lambdasonde"
+	#define MSG_HEATER_READY_1 "bereit"
+	#define MSG_HEATER_FAULT_0 "Lambdasonden-"
+	#define MSG_HEATER_FAULT_1 "heizung Fehler!"
+	#define MSG_HEATER_OFF_0 "Lambdasonde"
+	#define MSG_HEATER_OFF_1 "aus"
+	#define MSG_HEATER_CURRENT "Heizstrom"
 	#define MSG_TIME_SINCE_START "Zeit seit Start"
 
 #endif
diff --git a/lambda/pins.h b/lambda/pins.h
index 931b6cd..f307075 100644
--- a/lambda/pins.h
+++ b/lambda/pins.h
@@ -18,8 +18,8 @@
 #define ADC_TEMPO PC0
 /** ADC pin for the LSM 11 oxygen sensor signal */
 #define ADC_LAMBDA PC1
-/** ADC pin for the LSM 11 oxygen sensor heating current */
-#define ADC_HEATING PC3
+/** ADC pin for the LSM 11 oxygen sensor heater current */
+#define ADC_HEATER PC3
 
 /** Port for menu button, beeper and oxygen sensor heater */
 #define PORT PORTB
diff --git a/lambda/rules.c b/lambda/rules.c
index 9d801be..2fa7f47 100644
--- a/lambda/rules.c
+++ b/lambda/rules.c
@@ -17,7 +17,7 @@
 #define TONE 31
 
 uint8_t age = 0;
-int8_t dir = 0;
+FireDir dir = none;
 uint8_t airgate = 100;
 
 static Measurement rulesMeasMax = {0, 0, 2000, 0};
@@ -33,7 +33,7 @@
  */
 static void airgate50(bool* const fired, int8_t const dir,
 		Measurement const meas) {
-	if (! *fired && dir == DIR_BURN_UP && meas.tempI >= 500) {
+	if (! *fired && dir == firing_up && meas.tempI >= 500) {
 		airgate = 50;
 		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_AIRGATE_50_0), PSTR(""), false);
 		*fired = true;
@@ -46,7 +46,7 @@
  */
 static void airgate25(bool* const fired, int8_t const dir,
 		Measurement const meas) {
-	if (! *fired && dir == DIR_BURN_DOWN && meas.tempI < 800) {
+	if (! *fired && dir == burning_down && meas.tempI < 800) {
 		airgate = 25;
 		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_AIRGATE_25_0), PSTR(""), false);
 		*fired = true;
@@ -59,8 +59,8 @@
  */
 static void airgateClose(bool* const fired, int8_t const dir,
 		Measurement const meas) {
-	if (! *fired && dir == DIR_BURN_DOWN && meas.tempI < 450) {
-		setHeatingOn(false);
+	if (! *fired && dir == burning_down && meas.tempI < 450) {
+		setHeaterOn(false);
 		airgate = 0;
 		alert_P(BEEPS, LENGTH, TONE,
 				PSTR(MSG_AIRGATE_CLOSE_0), PSTR(""), false);
@@ -74,7 +74,7 @@
 static void tooRich(bool* const fired, int8_t const dir,
 		Measurement const meas) {
 	if (! *fired && meas.tempI > 100 && meas.lambda < 1200 &&
-			getHeatingState() == HEATING_READY && airgate < 100) {
+			getHeaterState() == heaterStateReady && airgate < 100) {
 		airgate = 100;
 		alert_P(BEEPS, LENGTH, TONE,
 				PSTR(MSG_TOO_RICH_0), PSTR(MSG_TOO_RICH_1), false);
@@ -91,7 +91,7 @@
 static void tooLean(bool* const fired, int8_t const dir,
 		Measurement const meas) {
 	if (! *fired && meas.tempI > 500 && meas.lambda > 1600 &&
-			getHeatingState() == HEATING_READY && airgate > 50) {
+			getHeaterState() == heaterStateReady && airgate > 50) {
 		airgate = 50;
 		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_AIRGATE_50_0), PSTR(""), false);
 		*fired = true;
@@ -106,7 +106,7 @@
  */
 static void fireOut(bool* const fired, int8_t const dir,
 		Measurement const meas) {
-	if (! *fired && dir == DIR_BURN_UP && meas.tempI < 100 &&
+	if (! *fired && dir == firing_up && meas.tempI < 100 &&
 			rulesMeasMax.tempI - meas.tempI > 25) {
 		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_FIRE_OUT_0), PSTR(""), false);
 		*fired = true;
@@ -117,49 +117,49 @@
 }
 
 /**
- * Notifies that the heating is ready and sets the corresponding state.
+ * Notifies that the heater is ready and sets the corresponding state.
  */
-static void heatingReady(bool* const fired, int8_t const dir,
+static void heaterReady(bool* const fired, int8_t const dir,
 		Measurement const meas) {
-	if (! isHeatingOn() || getHeatingState() == HEATING_READY) {
+	if (! isHeaterOn() || getHeaterState() == heaterStateReady) {
 		return;
 	}
-	if (meas.current <= HEATING_READY_MA && meas.current > HEATING_DISCONN_MA) {
-		setHeatingState(HEATING_READY);
-		alert_P(3, 10, TONE, PSTR(MSG_HEATING_READY_0),
-				PSTR(MSG_HEATING_READY_1), false);
+	if (meas.current <= milliAmpsReady && meas.current > milliAmpsDisconn) {
+		setHeaterState(heaterStateReady);
+		alert_P(3, 10, TONE, PSTR(MSG_HEATER_READY_0),
+				PSTR(MSG_HEATER_READY_1), false);
 	}
 }
 
 /**
- * Notifies that the heating or its connection is faulty and sets the
+ * Notifies that the heater or its connection is faulty and sets the
  * corresponding state.
  */
-static void heatingFault(bool* const fired, int8_t const dir,
+static void heaterFault(bool* const fired, int8_t const dir,
 		Measurement const meas) {
-	if (! isHeatingOn() || getHeatingState() == HEATING_FAULT) {
+	if (! isHeaterOn() || getHeaterState() == heaterStateFault) {
 		return;
 	}
-	if (meas.current > HEATING_SHORT_MA || meas.current < HEATING_DISCONN_MA ||
-			(getTime() >= 180 && meas.current > HEATING_READY_MA)) {
+	if (meas.current > milliAmpsShort || meas.current < milliAmpsDisconn ||
+			(getTime() >= 180 && meas.current > milliAmpsReady)) {
 		// short circuit or disconnected or did not warm up within 3 minutes
-		setHeatingOn(false);
-		setHeatingState(HEATING_FAULT);
-		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_HEATING_FAULT_0),
-				PSTR(MSG_HEATING_FAULT_1), true);
+		setHeaterOn(false);
+		setHeaterState(heaterStateFault);
+		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_HEATER_FAULT_0),
+				PSTR(MSG_HEATER_FAULT_1), true);
 	}
 }
 
 /**
- * Switches the heating off if it is still on after 3 hours and there does
+ * Switches the heater off if it is still on after 3 hours and there does
  * not seem to be a fire.
  */
-static void heatingTimeout(bool* const fired, int8_t const dir,
+static void heaterTimeout(bool* const fired, int8_t const dir,
 		Measurement const meas) {
-	if (isHeatingOn() && getTime() >= 10800 && meas.tempI < 400) {
-		setHeatingOn(false);
-		alert_P(3, 10, TONE, PSTR(MSG_HEATING_OFF_0),
-				PSTR(MSG_HEATING_OFF_1), false);
+	if (isHeaterOn() && getTime() >= 10800 && meas.tempI < 400) {
+		setHeaterOn(false);
+		alert_P(3, 10, TONE, PSTR(MSG_HEATER_OFF_0),
+				PSTR(MSG_HEATER_OFF_1), false);
 	}
 }
 
@@ -181,9 +181,9 @@
  * Heater rules applied to each not averaged measured heater current value
  */
 Rule heaterRules[] = {
-		{false, heatingReady},
-		{false, heatingFault},
-		{false, heatingTimeout}
+		{false, heaterReady},
+		{false, heaterFault},
+		{false, heaterTimeout}
 };
 
 
@@ -209,13 +209,13 @@
 	// try to figure out if the fire is building up or burning down by
 	// comparing current measurements with ones that are 3 minutes old.
 	if (age >= 180) {
-		dir = DIR_NONE;
+		dir = none;
 		if ((meas.tempI - rulesMeasPrev.tempI) >= 10 &&
 				rulesMeasMax.tempI < 800 && meas.lambda >= 2000) {
-			dir = DIR_BURN_UP;
+			dir = firing_up;
 		} else if ((rulesMeasPrev.tempI - meas.tempI) >= 1 &&
 				rulesMeasMax.tempI > 800 && meas.lambda >= 2000) {
-			dir = DIR_BURN_DOWN;
+			dir = burning_down;
 		}
 
 		rulesMeasPrev = meas;
@@ -234,7 +234,7 @@
 	rulesMeasMax.tempI = 0;
 
 	age = 0;
-	dir = DIR_NONE;
+	dir = none;
 	airgate = 100;
 
 	size_t rulesSize = sizeof(rules) / sizeof(rules[0]);
diff --git a/lambda/rules.h b/lambda/rules.h
index a3db885..0df4ed5 100644
--- a/lambda/rules.h
+++ b/lambda/rules.h
@@ -11,9 +11,11 @@
 #include <stdbool.h>
 #include "sensors.h"
 
-#define DIR_NONE 0
-#define DIR_BURN_UP 1
-#define DIR_BURN_DOWN -1
+typedef enum {
+	none = 0,
+	firing_up = 1,
+	burning_down = -1
+} FireDir;
 
 /**
  * An attempt to create some sort of rule "object".
diff --git a/lambda/sensors.c b/lambda/sensors.c
index b2ad47d..dee5abd 100644
--- a/lambda/sensors.c
+++ b/lambda/sensors.c
@@ -21,7 +21,7 @@
 #include "pins.h"
 #include "messages.h"
 
-static int8_t heatingState = HEATING_OFF;
+static HeaterState heaterState = heaterStateOff;
 
 /**
  * Table used to look up the lambda value at 12 V heater voltage
@@ -91,7 +91,7 @@
 	tempOVoltageAvg = tempOVoltage + tempOVoltageAvg -
 			((tempOVoltageAvg - 4) >> 3);
 
-	if (heatingState == HEATING_READY) {
+	if (heaterState == heaterStateReady) {
 		uint32_t lambdaVoltage = linADC(getVoltage(ADC_LAMBDA));
 		lambdaVoltageAvg = lambdaVoltage + lambdaVoltageAvg -
 				((lambdaVoltageAvg - 4) >> 3);
@@ -99,13 +99,13 @@
 		lambdaVoltageAvg = 44 << 3;
 	}
 
-	uint16_t heatingVoltage = linADC(getVoltage(ADC_HEATING));
+	uint16_t heaterVoltage = linADC(getVoltage(ADC_HEATER));
 
 	Measurement meas;
 	meas.tempI = toTempI(tempIVoltageAvg >> 3);
 	meas.tempO = toTempO(tempOVoltageAvg >> 3);
 	meas.lambda = toLambda(lambdaVoltageAvg >> 3);
-	meas.current = toCurrent(heatingVoltage);
+	meas.current = toCurrent(heaterVoltage);
 
 	return meas;
 }
@@ -191,25 +191,25 @@
 	}
 }
 
-void setHeatingOn(bool const on) {
+void setHeaterOn(bool const on) {
 	if (on) {
 		PORTB |= (1 << PB2);
-		heatingState = HEATING_UP;
-		alert_P(1, 2, 31, PSTR(MSG_HEATING_UP_0), PSTR(MSG_HEATING_UP_1), true);
+		heaterState = heaterStateUp;
+		alert_P(1, 2, 31, PSTR(MSG_HEATER_UP_0), PSTR(MSG_HEATER_UP_1), true);
 	} else {
 		PORTB &= ~(1 << PB2);
-		heatingState = HEATING_OFF;
+		heaterState = heaterStateOff;
 	}
 }
 
-bool isHeatingOn(void) {
+bool isHeaterOn(void) {
 	return bit_is_set(PORTB, PB2);
 }
 
-void setHeatingState(int8_t const state) {
-	heatingState = state;
+void setHeaterState(int8_t const state) {
+	heaterState = state;
 }
 
-int8_t getHeatingState(void) {
-	return heatingState;
+int8_t getHeaterState(void) {
+	return heaterState;
 }
diff --git a/lambda/sensors.h b/lambda/sensors.h
index ba77c5e..17b02f6 100644
--- a/lambda/sensors.h
+++ b/lambda/sensors.h
@@ -14,14 +14,25 @@
 #include <stdio.h>
 
 #define SHUNT_MILLIOHMS 100
-#define HEATING_READY_MA 1400
-#define HEATING_SHORT_MA 7500
-#define HEATING_DISCONN_MA 100
 
-#define HEATING_FAULT -1
-#define HEATING_OFF 0
-#define HEATING_UP 1
-#define HEATING_READY 2
+/**
+ * Oxygen sensor heater current limits at certain states in milliamps.
+ */
+typedef enum {
+	milliAmpsReady = 1400,
+	milliAmpsShort = 7500,
+	milliAmpsDisconn = 100
+} HeaterMilliAmps;
+
+/**
+ * Oxygen sensor heater states.
+ */
+typedef enum {
+	heaterStateFault = -1,
+	heaterStateOff = 0,
+	heaterStateUp = 1,
+	heaterStateReady = 2
+} HeaterState;
 
 /**
  * Entry for the lookup tables.
@@ -80,7 +91,7 @@
 uint16_t toLambda(uint16_t mV);
 
 /**
- * Returns the current of the oxygen sensor heating in mA.
+ * Returns the current of the oxygen sensor heater in mA.
  */
 uint16_t toCurrent(uint16_t mv);
 
@@ -105,24 +116,24 @@
 char* toInfo(uint16_t lambda);
 
 /**
- * Turns the heating of the oxygen sensor on or off.
+ * Turns the heater of the oxygen sensor on or off.
  */
-void setHeatingOn(bool on);
+void setHeaterOn(bool on);
 
 /**
- * Returns true if the heating of the oxygen sensor is turned on,
+ * Returns true if the heater of the oxygen sensor is turned on,
  * false otherwise.
  */
-bool isHeatingOn(void);
+bool isHeaterOn(void);
 
 /**
- * Sets the state of the heating of the oxygen sensor to the given value.
+ * Sets the state of the heater of the oxygen sensor to the given value.
  */
-void setHeatingState(int8_t state);
+void setHeaterState(int8_t state);
 
 /**
- * Returns the state of the heating of the oxygen sensor.
+ * Returns the state of the heater of the oxygen sensor.
  */
-int8_t getHeatingState(void);
+int8_t getHeaterState(void);
 
 #endif /* SENSORS_H_ */