I'll rewrite parent's statement to apply to timers and stopwatches:

> Any sensible time handling solution will round off toward the starting value.

So a stopwatch won't display "1" until a full second has elapsed, and will look like this for five seconds: "0...1...2...3...4...5!"

A timer won't display "4" until a full second has elapsed, and will look like this: "5...4...3...2...1...0!"

In the stopwatch case, the display shows "0" for 0.999 s; in the timer case it'll show "1" for 0.999 s.