Nerd version: the gaps between pings are described by an exponential

distribution, the expectation of which is the rate parameter (or

reciprocal of that, I forget), which is 45 minutes. So you can reduce

the variance slightly by using the *actual* gap between current and

previous ping but it’s going to converge to 45 minutes anyway and it

simplifies things to just treat it as a constant 45 minutes. For

example, this tool wouldn’t work if you tried to use actual gaps:

Thanks a lot! It’s the first time I see the exponential distribution

(whose expected value is parameter^{-1}, btw) in real life

Indeed, using the actual gap might make sense only at the very beginning,

when someone may think to be credited a wrong amount of time.

Even without going deeper in detail (that is, calling in the exponential

distribution) *over the long term* makes perfectly sense, because if some

pings are too close (extra credit), they will be compensated afterwards by

some other, more rare pings (too less credit).

PS: Actually I think I just proved to myself that it’s wrong to try to

use actual gaps.

I agree