diff --git a/lambda-test/lambda-test.c b/lambda-test/lambda-test.c
index 410f13f..8aa962f 100644
--- a/lambda-test/lambda-test.c
+++ b/lambda-test/lambda-test.c
@@ -62,14 +62,26 @@
 	// ADC interrupt enabled
 	assertTrue(bit_is_set(ADCSRA, ADIE));
 	// PC interrupts enabled
-	assertTrue(bit_is_set(PCICR, PCIE0));
-	assertTrue(bit_is_set(PCMSK0, PB0));
+	// assertTrue(bit_is_set(PCICR, PCIE0));
+	// assertTrue(bit_is_set(PCMSK0, PB0));
+	// enable timer 0 overflow interrupt
+	assertTrue(bit_is_set(TIMSK0, TOIE0));
 	// sei(); // enable global interrupts
 	assertTrue(bit_is_set(SREG, SREG_I));
 
 	return true;
 }
 
+bool testInitTimers(void) {
+	initInterrupts();
+
+	// timer clock prescaler /64 = 15.625 kHz overflowing every 16.2 ms
+	uint8_t prescalerBy64 = (1 << CS00) | (1 << CS01);
+	assertTrue((TCCR0B & prescalerBy64) == prescalerBy64);
+
+	return true;
+}
+
 /* Module adc */
 
 bool testSetupADC(void) {
@@ -292,6 +304,7 @@
 
 // TODO assertions
 bool testCycle(void) {
+	cycle();
 
 	return true;
 }
@@ -304,21 +317,28 @@
 
 // TODO assertions
 bool testUpdate(void) {
-	// set first display option so display() won't actually log something
-	// via USART which would break the test result XML
-	// TODO elegant solution for this and testing display()?
-
-	// measurement meas = {0, 0, 0, 0, 0, 0};
-	// update(meas);
+	measurement meas = {0, 0, 0, 0, 0, 0};
+	update(meas);
 
 	return true;
 }
 
-// these long function names passed along as strings use a lot of memory
+// TODO test display() with no display connected?
+bool testDisplay(void) {
+	measurement meas = {0, 0, 0, 0, 0, 0};
+	display(meas, "  ");
+
+	return true;
+}
+
+
+// TODO these long function names passed along as strings use a lot of memory
+// use PROGMEM?
 test tests[] = {
 		{"interrupts", "testSetupPorts", testSetupPorts},
 		{"interrupts", "testSetupSleepMode", testSetupSleepMode},
 		{"interrupts", "testInitInterrupts", testInitInterrupts},
+		{"interrupts", "testInitTimers", testInitInterrupts},
 		{"adc", "testSetupADC", testSetupADC},
 		{"adc", "testGetVoltage", testGetVoltage},
 		{"integers", "testDivRoundNearest", testDivRoundNearest},
@@ -345,7 +365,8 @@
 		{"sensors", "testToInfoRich", testToInfoRich},
 		{"display", "testCycle", testCycle},
 		{"display", "testUpdateInitial", testUpdateInitial},
-		{"display", "testUpdate", testUpdate}
+		{"display", "testUpdate", testUpdate},
+		{"display", "testDisplay", testDisplay}
 };
 
 int main(void) {
diff --git a/lambda/TODO b/lambda/TODO
index 439bafa..8e0c2d8 100644
--- a/lambda/TODO
+++ b/lambda/TODO
@@ -4,6 +4,4 @@
 
 * Functionality
 - Add beeper and beep when air gate valve should be closed and heating of
-  oxygen sensor should be switched off (or switch it off automatically?)
-- Add pushbutton to enter a menu
-  - Show min/max measurements of previous/current run?
\ No newline at end of file
+  oxygen sensor should be switched off (or switch it off automatically?)
\ No newline at end of file
diff --git a/lambda/display.c b/lambda/display.c
index 2ee0b08..6f4ff99 100644
--- a/lambda/display.c
+++ b/lambda/display.c
@@ -45,11 +45,11 @@
 	measMax.lambda = MAX(measMax.lambda, meas.lambda);
 
 	if (position == MENU_MIN_VALUES) {
-		display(measMin, "  <");
+		display(measMin, "|<");
 	} else if (position == MENU_MAX_VALUES) {
-		display(measMax, "  >");
+		display(measMax, ">|");
 	} else {
-		display(meas, "   ");
+		display(meas, "  ");
 	}
 }
 
@@ -62,7 +62,7 @@
 	printString(log);
 }
 
-void display(measurement meas, char hint[]) {
+void display(measurement meas, char* hint) {
 	uint16_t lambdax100 = divRoundNearest(meas.lambda, 10);
 	div_t lambdaT = div(lambdax100, 100);
 
diff --git a/lambda/display.h b/lambda/display.h
index 2128f3d..8dcc686 100644
--- a/lambda/display.h
+++ b/lambda/display.h
@@ -27,6 +27,6 @@
 /**
  * Formats the given measurement values and displays them on an 16x2 LCD.
  */
-void display(measurement, char[]);
+void display(measurement, char*);
 
 #endif /* DISPLAY_H_ */
diff --git a/lambda/interrupts.c b/lambda/interrupts.c
index 40797f6..8ad80d1 100644
--- a/lambda/interrupts.c
+++ b/lambda/interrupts.c
@@ -14,7 +14,7 @@
 	// INT0 and INT1 are assigned to the LCD, a bit of a shame
 	PORTB |= (1 << PB0);
 
-	// PB1 as output
+	// PB1 as output (just for testing)
 	DDRB |= (1 << PB1);
 }
 
diff --git a/lambda/lambda.c b/lambda/lambda.c
index e00635d..e81ec84 100644
--- a/lambda/lambda.c
+++ b/lambda/lambda.c
@@ -31,17 +31,15 @@
 #include "display.h"
 
 volatile bool buttonPressed = false;
-volatile uint8_t updateCount = 0;
-volatile uint8_t logCount = 0;
+volatile uint8_t intCount = 0;
 
 /**
  * Called every 16.32 ms.
  */
 ISR(TIMER0_OVF_vect) {
-	updateCount++;
-	logCount++;
+	intCount++;
 	if (bit_is_clear(PINB, PB0) && ! buttonPressed) {
-		PORTB ^= (1 << PB1);
+		// PORTB ^= (1 << PB1);
 		cycle();
 		buttonPressed = true;
 	} else if (bit_is_set(PINB, PB0)) {
@@ -64,14 +62,16 @@
 
 	// main loop
 	while (1) {
-		if (updateCount >= 6) {
-			updateCount = 0;
-			measurement meas = measure(); // about 50 ms
-			update(meas); // about 100 ms
-			if (logCount >= 61) {
-				logCount = 0;
-				print(meas); // about 400 ms
-			}
+		measurement meas;
+		if (intCount >= 60) {
+			intCount = 0;
+			meas = measure();
+			update(meas);
+			print(meas);
+		}
+		if (buttonPressed) {
+			// update display immediately
+			update(meas);
 		}
 	}