Serialprint is different if written first to variable

Projects Programming
6

Sorry for the missing declarations:

unsigned long timeold, timenew;
volatile long enc_count1=0;
bool set=false;
double rpm1=0;
double rpm_mittel1=0;

void setup() {
Serial.begin(115200);
  pinMode(2, INPUT_PULLUP);
  pinMode(3, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(2), count1, CHANGE);
  attachInterrupt(digitalPinToInterrupt(3), count1, CHANGE);
TCCR1B = TCCR1B & B11111000 | B00000001; 

}

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

   if(set==true){
    
    timeold = timenew;
    timenew = micros();
    rpm1 = double(double(enc_count1) * double(333333.33 / (timenew - timeold))); //60000000/180=333333,33
    set=false;
    Serial.println(rpm1);
    enc_count1=0;
      }
   
  analogWrite(6,100);

}

void count1()//ISR für den Hallsensor
{
  set=true;
  static int8_t lookup_table[] = {0, -1, 1, 0, 1, 0, 0, -1, -1, 0, 0, 1, 0, 1, -1, 0};
  static uint8_t enc_val1 = 0;
  enc_val1 = enc_val1 << 2;
  enc_val1 = enc_val1 | ((PIND & 0b1100) >> 2);
  enc_count1 = enc_count1 + lookup_table[enc_val1 & 0b1111];
  
  
}