Arduino code for 300zx accel gauge

//I wrote freq a lot below but really meant period.
uint16_t freqList[] = {5759,1920,960,576,384,274,206,160,128,105,87,74,63,55,48,42,38,34,30,27,25,23,21,19,18,16,15,14,13,12,12,11,10,10,9,9,8,8,7,7,7,6,6,6,6,5,5,5,5,5};
uint16_t lastFreqUpdate = 0;
uint16_t currentMSTimer = 0;
uint16_t updateTime = 100;
uint16_t currentIndex = 1;
uint16_t maxIndex = 49;
uint16_t activeFreq = 0;
uint16_t indexDir = 1;

void setup() {
  pinMode(13,OUTPUT);
  lastFreqUpdate=millis();
}

void loop() {
//one block of code needs to monitor for 100ms increments and update the current frequency
currentMSTimer = millis();
if(currentMSTimer - lastFreqUpdate > updateTime){
  if(indexDir==1 && currentIndex < maxIndex){
    currentIndex++;
  }  
  if(indexDir==0 && currentIndex > 0){
    currentIndex--;
  }
  if(currentIndex==0){indexDir=1;}
  if(currentIndex==maxIndex){indexDir=0;}
  activeFreq = freqList[currentIndex];
  lastFreqUpdate = currentMSTimer;
}
// second block of code needs to toggle the digital output at the proper frequency
 if((2*(currentMSTimer%activeFreq))>activeFreq){digitalWrite(13,HIGH);}
else{digitalWrite(13,LOW);}
}