XFORMAT = expr;          Set X axis fiducial label format

The value of 'expr' identifies one of three X axis fiducial label
formats; namely,

    NOMINAL  Label fiducials with floating point numbers.
    DATES    Label fiducials with dates of the form mm/dd/yy.
    HOURS    Label fiducials with time values in the form hh:mm:ss.

This control also affects the format of the time tag fields output
by the PRINT and WRITE procedures and the prompt for OPER
input.
