The command rmarc is for creating a 3 line truncation from an arc. The arc will need to be a polyline, this can
be done by pedit
Step 1
Make sure the arc is a polyline, if not then type pedit into the command line and select the arc to convert.
Step 2
Type rmarc into the command line
Step 3
Select the arc then if you want 3 (or more) chords
Step 4
Type c for count and 3 for the number of chords.
If you are using the command regularly, then a button can be created using *^C^C_rmarc;;count;3;@; in the
Macro.