In-game stopwatch

[siber]

Once again, apologies if this has been covered before, but my search for previous threads came up negative...

I noticed the other day that on the plotting screen there's a stopwatch and speed/distance charts for making plotting intercepts easier on the maths. That's great - makes the distances much easier to calculate - but I can't seem to make the watch work. Does it work, or is it just fold-away eye-candy? If so, how?

Thanks in anticipation of responses!