     for(size_t i = 0; i < countof(buttons); ++i) {
         pinMode(buttons[i], INPUT);           // set pin to input
         digitalWrite(buttons[i], HIGH);       // turn on internal pullup resistors
+
+        // Note that internal pull-up resistor switches the state of a button.
+        // To check if a button is pressed, test digitalRead(ButtonPin) == HIGH
     }
 
     clock_clearScreen();

void loop()
{
    for(size_t i = 0; i < countof(buttons); ++i) {
        Call(clock_button_press( &(clockState.buttons), i, digitalRead(buttons[i]) == HIGH ? TRUE : FALSE));
    }
    Call(clock_update(&clockState));

    display();
    delay(DUTY_CYCLE_MILLIS);
}


#define DUTY_CYCLE_MILLIS 13

#define BUTTON_1_PIN 2
#define BUTTON_2_PIN 3
#define BUTTON_3_PIN 4
#define BUTTON_4_PIN 5

// Pin connected to ST_CP of 74HC595
#define LATCH_PIN 8
