volatile unsigned int watts = 0;
const unsigned long wattMilliseconds = 5UL * 1000UL * 60UL * 60UL * 1000UL; // 5 kWh in watt milliseconds.
void ISR1()
{
static unsigned long previousPulseTime = 0;
unsigned long currentTime = millis();
unsigned long elapsedTime = currentTime - previousPulseTime;
previousPulseTime = currentTime;
watts = wattMilliseconds / elapsedTime;
}