diff --git a/encoder.c b/encoder.c
index 9ba66f6..0179632 100644
--- a/encoder.c
+++ b/encoder.c
@@ -9,18 +9,41 @@
 #include "encoder.h"
 #include "systick.h"
 
+/* Use the big slit on the rotary encoder to determine an absolute position
+   (modulo a full rotation) if defined */
 #define USE_CORRECTION
+/* If defined, use this value as value for the lowest detected position of the
+   big slit. If undefined, the value moves so the lowest seen value is 0. */
 #define FIXED_OFFSET 20
+/* Show lots of debug output */
 // #define DEBUG_ENCODER_TICKS
+/* Number of encoder changes to use for speed averaging */
 #define SPEED_AVG_NUM 4
 
+/* Number of slits in a full rotation */
+#define MARKS 96
+/* Port for both pins on the rotary encoder */
+#define PIN_PORT GPIOC
+/* The corresponding RCC */
+#define PIN_RCC RCC_GPIOC
+/* GPIO pin that rises first when opening the door */
+#define PIN_OPEN GPIO1
+/* Its interrupt */
+#define PIN_OPEN_IRQ NVIC_EXTI1_IRQ
+/* GPIO pin that rises first when closing the door */
+#define PIN_CLOSE GPIO2
+/* Its interrupt */
+#define PIN_CLOSE_IRQ NVIC_EXTI2_IRQ
+
 #ifdef DEBUG_ENCODER_TICKS
 #define LOG_ENCODER_DEBUG_TICKS(...) printf(__VA_ARGS__)
 #else
 #define LOG_ENCODER_DEBUG_TICKS(...)
 #endif
 
+/* Position */
 static volatile int pos = 0;
+/* Offset/value of the lowest seen positon of the long slit */
 static int offset =
   #ifdef FIXED_OFFSET
     FIXED_OFFSET
@@ -28,24 +51,23 @@ static int offset =
     -1
   #endif
   ;
+/* Rotation speed measured at the last position change */
 static volatile int speed = 0;
-static void check(void);
 
+/* Time of the last position change */
 static uint32_t last_tick = 0;
+/* Timestamp/position pairs for the last n positions (only measured when neither
+   pin is high). Last value contains just the position, without taking the long
+   slit into account, to prevent that from affecting the speed. */
 static struct tick_pos {
   uint32_t tick;
   int pos;
 } speed_ticks[SPEED_AVG_NUM + 1] = {0};
+/* Times for when one/both/the other pin is high, for detecting the long
+   slit. */
 static uint32_t ticks[3] = {0};
 
-#define MARKS 96
-#define PIN_OPEN GPIO1
-#define PIN_OPEN_IRQ NVIC_EXTI1_IRQ
-#define PIN_CLOSE GPIO2
-#define PIN_CLOSE_IRQ NVIC_EXTI2_IRQ
-
-#define PIN_PORT GPIOC
-#define PIN_RCC RCC_GPIOC
+static void check(void);
 
 void encoder_setup(void) {
         rcc_periph_clock_enable(PIN_RCC);