diff --git a/src/bus/i2c.c b/src/bus/i2c.c
index 3de6a19..d777187 100644
--- a/src/bus/i2c.c
+++ b/src/bus/i2c.c
@@ -3,26 +3,27 @@
 
 #include <avr/io.h>
 
-#define TW_START        0x08
-#define TW_REP_START    0x10
-#define TW_MT_SLA_ACK   0x18
-#define TW_MT_SLA_NACK  0x20
-#define TW_MT_DATA_ACK  0x28
-#define TW_MR_SLA_ACK   0x40
-#define TW_MR_SLA_NACK  0x48
-#define TW_MR_DATA_ACK  0x50
+#define TW_START       0x08  // Start condition transmitted
+#define TW_REP_START   0x10  // Repeated start condition transmitted
+#define TW_MT_SLA_ACK  0x18  // SLA+W transmitted, ACK received
+#define TW_MT_SLA_NACK 0x20  // SLA+W transmitted, NACK received
+#define TW_MT_DATA_ACK 0x28  // Data transmitted, ACK received
+#define TW_MR_SLA_ACK  0x40  // SLA+R transmitted, ACK received
+#define TW_MR_SLA_NACK 0x48  // SLA+R transmitted, NACK received
+#define TW_MR_DATA_ACK 0x50  // Data received, ACK returned
 
-// TODO: Error handling and recovery without watchdog timer.
-// TODO: Implement I2C_vect ISR? This may not actually be
+// TODO: Error handling and recovery besides watchdog timer.
+// TODO: Add more documentation from the atmel data sheet.
+// TODO: Implement TWI_vect ISR? This may not actually be
 // much better than the blocking approach.
 
-static void I2C_AHT20_Reset(void);
-static bool I2C_AHT20_IsCalibrated(void);
-static void I2C_AHT20_Calibrate(void);
-static void I2C_AHT20_Trigger(void);
+static void  I2C_AHT20_Reset(void);
+static bool  I2C_AHT20_IsCalibrated(void);
+static void  I2C_AHT20_Calibrate(void);
+static void  I2C_AHT20_Trigger(void);
 
-static int  I2C_ADS1115_WriteRegister(byte reg, word data);
-static word I2C_ADS1115_ReadRegister(byte reg);
+static int   I2C_ADS1115_WriteRegister(byte reg, word data);
+static word  I2C_ADS1115_ReadRegister(byte reg);
 
 int I2C_Init(void)
 {
@@ -516,13 +517,13 @@ word I2C_ADS1115_Read(int channel)
 	// 111  |  AINP = AIN3, AINN = GND
 
 	mux = 0;
-	if (channel == 0)
+	if (channel == ADS01)
 		mux = 0x4000; //     |  01000000 00000000
-	else if (channel == 1)
+	else if (channel == ADS02)
 		mux = 0x5000; //     |  01010000 00000000
-	else if (channel == 2)
+	else if (channel == ADS03)
 		mux = 0x6000; //     |  01100000 00000000
-	else if (channel == 3)
+	else if (channel == ADS04)
 		mux = 0x7000; //     |  01110000 00000000
 
 	// Single-shot conversion, active low, continous mode
diff --git a/src/bus/i2c.h b/src/bus/i2c.h
index ce004c1..10f0dff 100644
--- a/src/bus/i2c.h
+++ b/src/bus/i2c.h
@@ -8,6 +8,12 @@
 #define AHT02 0x1  // Middle
 #define AHT03 0x2  // Lower
 
+// ADC channels
+#define ADS01 0x0  // AIN0 GND
+#define ADS02 0x1  // AIN1 GND
+#define ADS03 0x2  // AIN2 GND
+#define ADS04 0x3  // AIN3 GND
+
 int   I2C_Init(void);
 int   I2C_Start(byte addr, byte mode);
 int   I2C_SetChannel(int channel);
diff --git a/src/main.c b/src/main.c
index d764866..49fb84f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -16,7 +16,7 @@
 // TODO: Write an improved command parser (low priority).
 // TODO: Proper error handling and recovery (after testing).
 
-int Init(void)
+static int Init(void)
 {
 	// MOSFETS control things like the heating element
 	// so they are the highest priority to initialize
@@ -94,7 +94,7 @@ int Init(void)
 	return 0;
 }
 
-void Update(void)
+static void Update(void)
 {
 	float temp[3], rh[3];
 	short adc[4];
@@ -110,10 +110,10 @@ void Update(void)
 	I2C_SetChannel(AHT03);
 	I2C_AHT20_Read(&temp[2], &rh[2]);
 
-	adc[0] = I2C_ADS1115_Read(0);
-	adc[1] = I2C_ADS1115_Read(1);
-	adc[2] = I2C_ADS1115_Read(2);
-	adc[3] = I2C_ADS1115_Read(3);
+	adc[0] = I2C_ADS1115_Read(ADS01);
+	adc[1] = I2C_ADS1115_Read(ADS02);
+	adc[2] = I2C_ADS1115_Read(ADS03);
+	adc[3] = I2C_ADS1115_Read(ADS04);
 
 	Info("TEMP0=%.2fC, RH0=%.2f%%", temp[0], rh[0]);
 	Info("TEMP1=%.2fC, RH1=%.2f%%", temp[1], rh[1]);