It's hardly abstract, it's elementary my dear Citizen. No. Really. It's single-digit decimals. You're adding uneven halves by going from 1-5 and then from 5-10.
OK, you say that a 1/10 can be the worst someone's seen on Imdb. However, the thing is that Imdb does not allow us to address 0 quality (I've seen many 0's in my life), so the math needs to be adjusted if 0 is to be technically included for Imdb. For MoFo, we do have a
option, so 0 is our starting point. So to get from 0-10, we add five and then five again.
0 = Lust for Frankenstein
5 = The Golem
10 = The Godfather
True, this means that we have 11 numbers, 1-10 and 0, but 0 means absolutely no quality. Since Imdb does not allow us to address 0 quality, than 1 is acting on 0's behalf, so we need to adjust the meter and the math that goes with it. This is part of why I prefer MoFo to Imdb. It allows 0-star ratings. Now if only Letterboxd would.
We don't have to "actually adjust all our ratings," but to get a halfway point, you do need to adjust the math. Halfway to the minimum is halfway to the maximum. So halfway from 0-10 is 5, and 1 is our minimum, and not 0, then instead of taking 10 "spaces" to get to 10, we need 1 less. 9. So what's half of 9? Add that to the minimum and you get the halfway point.
The minimum (x) for MoFo: 0.
The Maximum (y) for Mofo: 10
Subtract the maximum from the minimum: y - x = 10 - 0 = 10
Half of the maximum is 5.
Thus, the halfway point is (y - x) / 2 + x = (10 - 0) / 2 + 0 = 5
The minimum (x) for Imdb: 1.
The Maximum (y) for Imdb: 10
Subtract the maximum from the minimum: y - x = 10 - 1 = 9
Half of the maximum is 4.5.
Thus, the halfway point is (y - x) / 2 + x = (10 - 1) / 2 + 1 = 5.5
Does your brain hurt yet?