Date range duration

The span between two dates expressed every way at once — years, months and days, plus the totals in days, weeks, months and hours.

Having every unit at once avoids the commonest mistake in date arithmetic, which is quoting a figure in the wrong one. "Three months" and "90 days" are different spans and a contract that uses them interchangeably has a problem; showing both makes the difference visible rather than something you have to remember to check. The direction field matters for the same reason: reversing the dates gives the same magnitude with the opposite sign, and a duration that comes out negative usually means the inputs are the wrong way round rather than that anything is wrong with the arithmetic.