http://search.cpan.org/~sbeck/Date-Manip-6.56/lib/Date/Manip/Calc.pod

Exact, semi-exact, and approximate calculations An exact calculation is one in which the delta used (or produced) is an exact delta. An exact delta is described in the Date::Manip::Delta manual, but the short explanation is that it is a delta which only involves fields of an exactly known length (hours, minutes, and seconds). Business deltas also include days in the exact part. The value of all other fields in the delta will be zero. ... $mode defaults to "exact".

Why the mode seems to be different between the versions i cannot say

A semi-exact calculation is one in which the deltas used (or produced) is a semi-exact delta. This is also described in the Date::Manip::Delta manual, but the short explanation is that it includes days and weeks (for standard calculations) or weeks (for business calculations) in addition to the exact fields.

Edit to add: Ah the mode change is explained in the reply by SBECK in the post that hippo referenced above, i knew i saw something before but couldnt find it

In reply to Re: DateCalc using Date::Manip by huck
in thread DateCalc using Date::Manip by tsdesai

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