int16_t time_is, time_mem1;

loop()
{
   time_is = (int16_t) millis();

   // compare as "signed int" to get rid of glitches when the variable overflows

   if ((signed)(time_is-time_mem1-1000)>=0)
   {
      time_mem1 = time_is;
      // function below is executed every second
      my_display();
   }

}