diff --git a/lambda-test/rules-test.c b/lambda-test/rules-test.c
index 2746ba6..527719f 100644
--- a/lambda-test/rules-test.c
+++ b/lambda-test/rules-test.c
@@ -148,7 +148,6 @@
 
 	meas.tempI = 99;
 	meas.lambda = 2000;
-
 	resetRules();
 	reason(meas);
 	assertFalse(rules[3].fired);
@@ -162,21 +161,18 @@
 
 	meas.tempI = 99;
 	meas.lambda = 1199;
-
 	resetRules();
 	reason(meas);
 	assertFalse(rules[3].fired);
 
 	meas.tempI = 100;
 	meas.lambda = 1199;
-
 	resetRules();
 	reason(meas);
 	assertTrue(rules[3].fired);
 
 	meas.lambda = 1300;
 	age = 0;
-
 	reason(meas);
 	assertFalse(rules[3].fired);
 
@@ -192,31 +188,26 @@
 	dir = 1;
 
 	meas.tempI = 50;
-
 	age = 0;
 	reason(meas);
 	assertFalse(rules[4].fired);
 
 	meas.tempI = 100;
-
 	age = 0;
 	reason(meas);
 	assertFalse(rules[4].fired);
 
 	meas.tempI = 125;
-
 	age = 0;
 	reason(meas);
 	assertFalse(rules[4].fired);
 
 	meas.tempI = 99;
-
 	age = 0;
 	reason(meas);
 	assertTrue(rules[4].fired);
 
 	meas.tempI = 125;
-
 	age = 0;
 	reason(meas);
 	assertFalse(rules[4].fired);
@@ -226,6 +217,112 @@
 	return true;
 }
 
+bool testReasonDirBurnUp(void) {
+
+	resetRules();
+	Measurement meas = {0, 0, 2000};
+
+	age = 0;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	meas.tempI = 9;
+	meas.lambda = 2000;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	meas.tempI = 100;
+	meas.lambda = 2000;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 1);
+
+	meas.tempI = 790;
+	meas.lambda = 2000;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 1);
+
+	meas.tempI = 790;
+	meas.lambda = 2000;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	meas.tempI = 800;
+	meas.lambda = 2000;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 1);
+
+	meas.tempI = 850;
+	meas.lambda = 2000;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	meas.tempI = 900;
+	meas.lambda = 1999;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	cancelAlert();
+
+	return true;
+}
+
+bool testReasonDirBurnDown(void) {
+
+	resetRules();
+	Measurement meas = {999, 0, 1999};
+
+	age = 0;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	meas.tempI = 900;
+	meas.lambda = 1999;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	meas.tempI = 800;
+	meas.lambda = 1999;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	meas.tempI = 750;
+	meas.lambda = 1999;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	meas.tempI = 700;
+	meas.lambda = 2000;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == -1);
+
+	meas.tempI = 700;
+	meas.lambda = 2000;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == 0);
+
+	meas.tempI = 100;
+	meas.lambda = 2000;
+	age = 180;
+	reason(meas);
+	assertTrue(dir == -1);
+
+	cancelAlert();
+
+	return true;
+}
+
 /* Test "class" */
 static const char class[] PROGMEM = "rules";
 
@@ -235,6 +332,8 @@
 static const char testAirgateClose_P[] PROGMEM = "testAirgateClose";
 static const char testTooRich_P[] PROGMEM = "testTooRich";
 static const char testFireOut_P[] PROGMEM = "testFireOut";
+static const char testReasonDirBurnUp_P[] PROGMEM = "testReasonDirBurnUp";
+static const char testReasonDirBurnDown_P[] PROGMEM = "testReasonDirBurnDown";
 
 /* Tests */
 static TestCase const tests[] = {
@@ -242,7 +341,9 @@
 		{class, testAirgate25_P, testAirgate25},
 		{class, testAirgateClose_P, testAirgateClose},
 		{class, testTooRich_P, testTooRich},
-		{class, testFireOut_P, testFireOut}
+		{class, testFireOut_P, testFireOut},
+		{class, testReasonDirBurnUp_P, testReasonDirBurnUp},
+		{class, testReasonDirBurnDown_P, testReasonDirBurnDown}
 };
 
 TestClass rulesClass = {tests, sizeof(tests) / sizeof(tests[0])};
diff --git a/lambda/rules.c b/lambda/rules.c
index 906c7b2..129d119 100644
--- a/lambda/rules.c
+++ b/lambda/rules.c
@@ -19,11 +19,12 @@
 #define DIR_BURN_UP 1
 #define DIR_BURN_DOWN -1
 
-Measurement rulesMeasMax = {0, 0, 2000};
-Measurement rulesMeasPrev = {0, 0, 2000};
 uint16_t age = 0;
 int8_t dir = 0;
 
+static Measurement rulesMeasMax = {0, 0, 2000};
+static Measurement rulesMeasPrev = {0, 0, 2000};
+
 /**
  * Reminds to set the air gate to 50% when the fire is still building up
  * and the temperature has reached 500°C.
@@ -114,6 +115,8 @@
 		}
 	}
 
+	age++;
+
 	// 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) {
@@ -133,8 +136,6 @@
 	rulesMeasMax.tempI = MAX(rulesMeasMax.tempI, meas.tempI);
 	rulesMeasMax.tempO = MAX(rulesMeasMax.tempO, meas.tempO);
 	rulesMeasMax.lambda = MIN(rulesMeasMax.lambda, meas.lambda);
-
-	age++;
 }
 
 void resetRules(void) {