diff --git a/main.c b/main.c
index 68f41d5..865b60b 100644
--- a/main.c
+++ b/main.c
@@ -51,7 +51,7 @@ const float gVoltageScale[VOLTAGE_SCALES] = {
 
 uint32_t cputime_unloaded;
 
-int RisingTrigger(void);
+int Trigger(bool rising);
 
 // start a pwm test signal
 void start_signal() {
@@ -129,6 +129,7 @@ int main(void) {
     IntMasterEnable();
 
     uint8_t voltage_scale = 0;
+    uint8_t rising = 1;
 
     while (true) {
         // calculate cpu usage
@@ -141,6 +142,9 @@ int main(void) {
         Button button = (Button) 0;
         while (fifo_get(&button)) {
             switch (button) {
+                case S1: // toggle edge
+                    rising = !rising;
+                    break;
                 case S2: // draw
                     refresh = !refresh;
                     break;
@@ -175,13 +179,19 @@ int main(void) {
         snprintf(str, sizeof(str), "CPU Load %.1f%%", usage_percent); 
         GrStringDraw(&sContext, str, /*length*/ -1, /*x*/ 0, /*y*/ HEIGHT - 10, /*opaque*/ false);
 
+        if (rising) {
+            GrStringDraw(&sContext, "^", /*length*/ -1, /*x*/ WIDTH - 10, /*y*/ 0, /*opaque*/ false);
+        } else {
+            GrStringDraw(&sContext, "v", /*length*/ -1, /*x*/ WIDTH - 10, /*y*/ 0, /*opaque*/ false);
+        }
+
         // display graph
         #define LOCAL_BUF_LEN 128
         uint16_t local_adc_buffer[LOCAL_BUF_LEN]; // copy of adc buffer
         int32_t adc_current_index;
         int32_t j;
         if (refresh) {
-            int trigger = RisingTrigger();
+            int trigger = Trigger(rising);
 
             adc_current_index = trigger - (WIDTH / 2);
             for (j=0; j<LOCAL_BUF_LEN; j++) {
@@ -251,14 +261,22 @@ int main(void) {
     }
 }
 
-int RisingTrigger(void) // search for rising edge trigger
+int Trigger(bool rising) // search for edge trigger
 {
     int x = gADCBufferIndex - (WIDTH / 2); // half screen width
     int x_stop = x - ADC_BUFFER_SIZE/2;
     for (; x > x_stop; x--) {
-    if ( gADCBuffer[ADC_BUFFER_WRAP(x)] >= ADC_OFFSET &&
-        gADCBuffer[ADC_BUFFER_WRAP(x-1)] < ADC_OFFSET)
-        break;
+        if (rising) {
+            if ( gADCBuffer[ADC_BUFFER_WRAP(x)] >= ADC_OFFSET &&
+                gADCBuffer[ADC_BUFFER_WRAP(x-1)] < ADC_OFFSET) {
+                break;
+            }
+        } else { // falling edge trigger
+            if ( gADCBuffer[ADC_BUFFER_WRAP(x)] <= ADC_OFFSET &&
+                gADCBuffer[ADC_BUFFER_WRAP(x-1)] > ADC_OFFSET) {
+                break;
+            }
+        }
     }
     if (x == x_stop) // for loop ran to the end
     x = x = gADCBufferIndex - (WIDTH / 2); // reset x back to how it was initialized