244/310 = 0.79.
i.e. about 4/5 of the way up the building, which is a much more sensible place for a viewing platform of the tallest building in Europe.
1/3 (~100m) up would barely be worth the bother. Tower 42 (AKA the NatWest Tower) is 183m tall.
Even if it's 244m, the last 60m aren't going to be much use to anyone if it's that skinny at 244m