Return to Answer

The correct way to manage (or rather, avoid having to manage) the rollover problem is to think of the unsigned long number returned by millis() in terms of modular arithmetics. For the mathematically inclined, some familiarity with this concept is very useful when programming. You can see the math in action in Nick Gammon's article millis() overflow ... a bad thing?. For the problem at hand, what's important to know is that in modular arithmetics the numbers "wrap around" when reaching a certain value – the modulus – so that 1 − modulus is not a negative number but 1 (think of a 12 hour clock where the modulus is 12:01 − 12:00 ≡ 0:01).

The correct way to manage (or rather, avoid having to manage) the rollover problem is to think of the unsigned long number returned by millis() in terms of modular arithmetics. For the mathematically inclined, some familiarity with this concept is very useful when programming. You can see the math in action in Nick Gammon's article millis() overflow ... a bad thing?. For the problem at hand, what's important to know is that in modular arithmetics the numbers "wrap around" when reaching a certain value – the modulus – so that 1 − modulus is not a negative number but 1 (think of a 12 hour clock where the modulus is 12: here 1 − 12 = 1).

The correct way to manage (or rather, avoid having to manage) the rollover problem is to think of the unsigned long number returned by millis() in terms of modular arithmetics. For the mathematically inclined, some familiarity with this concept is very useful when programming. You can see the math in action in Nick Gammon's article millis() overflow ... a bad thing?. For the problem at hand, what's important to know is that in modular arithmetics the numbers "wrap around" when reaching a certain value – the modulus – so that 1 − modulus is not a negative number but 1 (think of a 12 hour clock where the modulus is 12: 1 − 12 = 1).

The correct way to manage (or rather, avoid having to manage) the rollover problem is to think of the unsigned long number returned by millis() in terms of modular arithmetics. For the mathematically inclined, some familiarity with this concept is very useful when programming. You can see the math in action in Nick Gammon's article millis() overflow ... a bad thing?. For the problem at hand, what's important to know is that in modular arithmetics the numbers "wrap around" when reaching a certain value – the modulus – so that 1 − modulus is not a negative number but 1 (think of a 12 hour clock where the modulus is 12:01 − 12:00 ≡ 0:01).

The correct way to manage (or rather, avoid having to manage) the rollover problem is to think of the unsigned long number returned by millis() in terms of modular arithmetics. For the mathematically inclined, some familiarity with this concept is very useful when programming. You can see the math in action in Nick Gammon's article millis() overflow ... a bad thing?. For the problem at hand, what's important to know is that in modular arithmetics the numbers "wrap around" when reaching a certain value - the modulus - so that 1 - modulus is not a negative number but 1 (think of a 12 hour clock where the modulus is 12: 1 - 12 = 1).

The correct way to manage (or rather, avoid having to manage) the rollover problem is to think of the unsigned long number returned by millis() in terms of modular arithmetics. For the mathematically inclined, some familiarity with this concept is very useful when programming. You can see the math in action in Nick Gammon's article millis() overflow ... a bad thing?. For the problem at hand, what's important to know is that in modular arithmetics the numbers "wrap around" when reaching a certain value – the modulus – so that 1 − modulus is not a negative number but 1 (think of a 12 hour clock where the modulus is 12: 1 − 12 = 1).