I saw these details in the INSTALL.txt of the Date::Calc module.

Prerequisites:

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Perl version 5.000 or higher, and an ANSI C compiler. (!)
^^^^^^
If you plan to use the modules "Date::Calendar" or "Date::Calendar::Year" from this package, you will also need the module "Bit::Vector" version 5.7 or newer (which also needs an ANSI C compiler!).

Otherwise you may safely ignore the warning message "Warning: prerequisite Bit::Vector 5.7 not found at ..." when running "perl Makefile.PL".

You can install "Bit::Vector" at any time later if you change your mind.

I do not plan to use the Calender & Year modules