 volatile int cycleNum = 666;
 volatile boolean mirrorTTL1 = true; // This is usually for varying systematics
 volatile boolean mirrorTTL2 = true; // Used for mirroring the Clock Bias field on/off
-volatile int mirrorTTL3source = 10; // 10 - source for beta shutter for polarized sequence
-                                    // 11 - source for beta shutter for unpolarized sequence
+volatile int mirrorTTL3source = pinTTL_IN3_pol; // 10 - source for beta shutter for polarized sequence
+                                                // 11 - source for beta shutter for unpolarized sequence
 
 void setup(){
   Serial_Init();

  pinMode(pinLCWaveplate, OUTPUT);
  pinMode(pinTTL_IN1, INPUT);
  pinMode(pinTTL_OUT1, OUTPUT);
  pinMode(pinClockTTL, OUTPUT);
  attachInterrupt(0, changeStartCOM, RISING);
  attachInterrupt(1, advanceCycleNum, RISING);

  else if (mode == 4){
    mirrorTTL1 = true;
    mirrorTTL2 = false; //Leave clock bias field off
    mirrorTTL3source = pinTTL_IN3_Upol; //Use unpolarized beta shutter protocol
  }
  else {
    mirrorTTL1 = true;
