The unit is a block
A rental engine thinks in whole days. It takes a first day and a last day and multiplies, which is right for a week on a canal boat and wrong for a sloop that leaves at nine, is back by one and goes out again at half past.
So a half-day is set up as a length of time at a price — 09:00, four hours, one number — and four sloops means four parties can take that same nine o'clock. The fifth is refused rather than taken and apologised for.




