Question

At the National Physical Laboratory in England, a measurement of the free-fall acceleration g was made by throwing a glass ball straight up in an
evacuated tube (the air was pumped out) and letting the ball return. Let ΔTL in the figure below be the time interval between the two passages of the ball across a certain lower level, ΔTU the time interval between the two passages across an upper level, and H the distance between the two levels.

What is ||g|| in terms of the measurements taken?