When choosing an adjective to refer to the nature of a calendar system, such as how we have months of varying length, is it more appropriate to use calendric or calendrical? Is there any difference, perhaps in context? Or is it a British vs American English thing?
The OED has only one entry for both words: there is no difference between them other than the one being a syllable longer than the other.
Laconic lovers of brevity who try never to use an -ical word when the corresponding -ic one will do would surely select the lighter calendric.
On the other hand, prolix writers and stentorian speakers of a more long-winded bent take precisely the opposite position — and, conflating length of discourse with quality, choose therefore the gratuitously heavier and more ponderous calendrical.
The choice is yours.