diff --git a/lib/7segment_4digits.c b/lib/7segment_4digits.c
index e4d24ed..932c9a0 100644
--- a/lib/7segment_4digits.c
+++ b/lib/7segment_4digits.c
@@ -28,11 +28,14 @@ void set_display_value(uint8_t digit, uint8_t data) {
     display[digit] = data;
 }
 
-void update_display() {
+// Returns the amount of microseconds we blocked for
+float update_display() {
+    int sleep_time = 2000;
     for (int i = 0; i < 4; i++) {
         display_value(i, display[i]);
-        _delay_us(100);
+        _delay_us(sleep_time);
     }
+    return sleep_time * 4;
 }
 
 void show_float(float value) {
diff --git a/lib/7segment_4digits.h b/lib/7segment_4digits.h
index ae54034..9d342ed 100644
--- a/lib/7segment_4digits.h
+++ b/lib/7segment_4digits.h
@@ -4,6 +4,6 @@ void display_value(uint8_t digit, uint8_t data);
 
 void set_display_value(uint8_t digit, uint8_t data);
 
-void update_display();
+float update_display();
 
 void show_float(float value);
diff --git a/main.c b/main.c
index 51e7fb0..fead234 100644
--- a/main.c
+++ b/main.c
@@ -40,16 +40,28 @@ void prog_7segment() {
 }
 
 void prog_7segment_4digit() {
-    DDRF = 0b11111111;
-    DDRK = 0b00001111;
+    DDRF  = 0b11111111;
+    DDRK  = 0b00001111;
+    PORTK = 0b10000000; // set pull-up
 
     float num = 0.0f;
+    bool running = false;
+    bool pressed = false;
 
     while(1) {
         show_float(num);
-        update_display();
+        float sleep_time = update_display();
 
-        num += 0.001f;
-        if (num >= 10000) num = 0.0f;
+        if (!pressed && bit_is_clear(PINK, PINK7)) {
+            running = !running;
+            pressed = true;
+        } else if (pressed && bit_is_set(PINK, PINK7)) {
+            pressed = false;
+        }
+
+        if (running) {
+            num += sleep_time / 1000.0f / 1000.0f;
+            if (num >= 10000) num = 0.0f;
+        }
     }
 }