     ShowTime_ms = TickTime;
     InterruptState = IRQ_NONE;
 
-    attachInterrupt (0, WheelRev, RISING);//pin 2 on Mega
+    attachInterrupt (1, WheelRev, RISING);//pin 3 on Mega
     SerialMonitor.print("TickTime: ");
     SerialMonitor.print(TickTime);
     SerialMonitor.print(" OldTick: ");

    pinMode(13, OUTPUT); //led
    digitalWrite(13, LOW);//turn LED off
    
    pinMode(2, INPUT);//pulls input HIGH
    float MinTick = WHEEL_DIAMETER_MM * PI;
//    SerialMonitor.print (" MinTick = ");
//    SerialMonitor.println (MinTick);

unsigned long MinTickTime_ms;
// ((WHEEL_DIAMETER_MM * 3142) / MAX_SPEED_mmPs)
// MinTickTime_ms = 89 ms
#define MIN_SPEED_mPh 3000
// A speed of less than 0.5 KPH is zero.
unsigned long MaxTickTime_ms;
// ((WHEEL_DIAMETER_MM * 3142) / MIN_SPEED_mmPs)
