ERROR
cal -M
Usage: cal [general options] [-jy] [[month] year]
<error message>
ncal -M
<displays ok>
SUGGESTION
In manual page, please mark all options that work only in ncal(1)
Like:
-M [ncal] Weeks start on Monday.
INFORMATION
man cal
-M Weeks start on Monday.
ls -l /usr/share/man/man1/cal.1.gz
lrwxrwxrwx 1 root root 9 2021-02-15 12:31 /usr/share/man/man1/cal.1.gz -> ncal.1.gz
ls -la /usr/bin/cal
lrwxrwxrwx 1 root root 4 2021-02-15 12:31 /usr/bin/cal -> ncal
ncal:
Installed: 12.1.7+nmu2
Candidate: 12.1.7+nmu2