calendar-split-width-threshold

calendar-split-width-threshold is a variable defined in `calendar.el'.
Its value is

nil

Documentation:
Value to use for `split-width-threshold' when creating a calendar.
This only affects frames wider than the default value of
`split-width-threshold'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.2 of Emacs.