Function: ruler-mode

Toggle display of ruler in header line (Ruler mode).
With a prefix argument ARG, enable Ruler mode if ARG is positive,
and disable it otherwise. If called from Lisp, enable the mode
if ARG is omitted or nil.

(fn &optional ARG)

Variable: ruler-mode

Non-nil if Ruler mode is enabled.
Use the command `ruler-mode' to change this variable.