millis() function returns the number of milliseconds the current sketch has been running since the last reset.

millis() returns an unsigned long.

#define MEASURE_INTERVAL 1000   // 
#define SEND_INTERVAL 16000   // 

unsigned long previous_millis_measure = 0;
unsigned long previous_millis_send = 0;

boolean measure_state = false;
boolean send_state = false;

void loop(void) 
{
  unsigned long current_millis = millis();
  
  if ((unsigned long)(current_millis - previous_millis_measure) >= MEASURE_INTERVAL)
  {
    measure_state = true;
    previous_millis_measure = current_millis;
  }

  if ((unsigned long)(current_millis - previous_millis_send) >= SEND_INTERVAL)
  {
    send_state = true;
    previous_millis_send = current_millis;
  }

  if (measure_state){ // == if true
    // measure something
    measure_state = false;
  }

 
  if (send_state){ // == if true
    // send something
    send_state = false;
  }

}