measureMSec

#define inputPin 3
unsigned long mSec;
unsigned long oldMillis;
unsigned char oldInput;

void setup() {
  // put your setup code here, to run once:
  pinMode( inputPin, INPUT_PULLUP);
  Serial.begin(115200);
  oldMillis= millis();
  oldInput= digitalRead( inputPin);
}

void loop() {
  // put your main code here, to run repeatedly:

  unsigned char inputNow= digitalRead( inputPin);
  if (oldInput!= inputNow) {
    unsigned long millisNow= millis();
    mSec= millisNow- oldMillis;
    oldMillis= millisNow;
    oldInput= inputNow;
    Serial.print( mSec);
    Serial.write( "\n");
  }
}