4 ms·

> The man with two watches knows that one of them is wrong, but only the man with three watches knows what time it really is. I realize it's an off-topic nitpi

• wolfgke 10y ago
  > I realize it's an off-topic nitpick, but that's not actually true. You take the average of all watches, and this will be your best guess for what time it really is. This only holds under additional assumptions, as for example that the errors of the watches are independent and normally distributed. In general this is not a good idea.
  • stdbrouw 10y ago
    If you know that errors are dependent or if you know the distribution of the error, you can make an even better guess, but that certainly doesn't make averaging "in general not a good idea." You're going to make assumptions whatever way you do it, e.g. using confirmation (two watches indicating the same time) to indicate truth assumes that error is fairly rare (out of 3 watches only 1 will be wrong at any given time) and that it's discontinuous rather than a smooth drift over time. No assumptions, no conclusions. Main point: more watches is always better, and three is not a magic number.