Well it had to get ahead somehow didn’t it? If we assuming that a clock was at some point set to the correct time and we then notice that it’s ahead, it would be fair to say that it is fast. The clock on my car radio is slow, literally.
Oh, sure, confuse a perfectly good semantic nitpick through the introduction of facts.
… but, unless their owner has specifically set them ahead, a clock that’s ahead will be so because it is fast - i.e., it will go on getting further and further ahead.
That may be less common now that everything is digital, but myself and Dad used to make our wristwatches run slow, while Mom’s would run fast.
The clock in my bathroom is fast, literally. I still haven’t learned not to panic thinking I’m running late (not literally running).
Yours too?!
I’ve been patiently biding my time, just waiting for the opportunity to use that one myself. 