I imagine it is a light aircraft thing, of which I have no experience. I know that some types of compasses used for sailing are biased for the area where they are sold and can need modifying if used in areas with significantly differing angles of dip.
On large aircraft, the standby compass is constructed so as the centre of gravity of the rotating assembly with the compass card attached is below the pivot point, so countering dip in either direction – hence, only one part number in the IPC.