Comparing two output

Projects Programming
7

now i just put

 Serial.println("------------------------"); 
  Serial.println(Tx); 
  
  Serial.println(f); 
Serial.println(m);

and noticed that the output is like this :

1476.62
1476.62
1

1476.62
1476.62
1

1476.62
1476.62
1

1476.62
1476.62
1

1476.62
1476.62
1

but when i compile below code

volatile float Tx = 0 ;

volatile float f = 0 ;

volatile float t = 0 ;
 
volatile int m = 0 ;

void setup() {
 
  Serial.begin(19200);
   Serial3.begin(38400);

  capture_pin2.config(CAPTURE_TIME_WINDOW);
attachInterrupt(digitalPinToInterrupt(2), measure , LOW );

}

void measure (){
  uint32_t status,duty,period;
  status=capture_pin2.get_duty_and_period(duty,period);

 t = (static_cast<double>(duty)/static_cast<double>(capture_pin2.ticks_per_usec()) );
  if ( (t > 1400) && (t < 1600))
{  Tx = t ;}

 }
void loop() {

  delay(20) ;

Serial.println(Tx); 

//-------------------------------------------------------------------

Tx keep changing.

do you have any idea why it doesn't change when i compile the main code that's mentioned at the begining.