Why does pulse sensor shows gaps when I move it? I modified the serial code in this way and I don't think the gap is produced by my edit even because it made it even before:

//////////
/////////  All Serial Handling Code, 
/////////  It's Changeable with the 'serialVisual' variable
/////////  Set it to 'true' or 'false' when it's declared at start of code.  
/////////

void serialOutput(){   // Decide How To Output Serial. 
 if (serialVisual == true){  
     arduinoSerialMonitorVisual('-', Signal);   // goes to function that makes Serial Monitor Visualizer
 } else{
      sendDataToSerial('S', Signal);     // goes to sendDataToSerial function
 }        
}


//  Decides How To OutPut BPM and IBI Data
void serialOutputWhenBeatHappens(){    
 if (serialVisual == true){            //  Code to Make the Serial Monitor Visualizer Work
    //ASCII Art Madness
    Serial.print(BPM);
    Serial.println("");

 } else{
        sendDataToSerial('B',BPM);   // send heart rate with a 'B' prefix
        sendDataToSerial('Q',IBI);   // send time between beats with a 'Q' prefix
 }   
}



//  Sends Data to Pulse Sensor Processing App, Native Mac App, or Third-party Serial Readers. 
void sendDataToSerial(char symbol, int data ){
    Serial.print(symbol);

    Serial.println(data);                
  }


//  Code to Make the Serial Monitor Visualizer Work
void arduinoSerialMonitorVisual(char symbol, int data ){    
  const int sensorMin = 0;      // sensor minimum, discovered through experiment
const int sensorMax = 1024;    // sensor maximum, discovered through experiment

  int sensorReading = data;
  // map the sensor range to a range of 12 options:
  int range = map(sensorReading, sensorMin, sensorMax, 0, 11);

  // do something different depending on the 
  // range value:
  switch (range) {
  case 0:     
    Serial.println("");

  } 
}



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You can find all the code here:
https://github.com/WorldFamousElectronics/PulseSensor_Amped_Arduino

In the code I posted there is some code I don'f find useful but I can't delete it for reason linked to variables used for other functions I don't know I'm using.
You can also see huge changes in the heart rate that surely don't reflect the reality.
One of the possibilities is when you move your finger, the sensor grip loosened and doesn't count a "beat". So the sensor emits data = 0, and it will cause 

Serial.println("");    


in your switch-case.