I too can remember this; and I used a paperclip on an upside down styrofoam cup on a ballpoint pen to demonstrate this when I was instructing.
The Instrument Flying Handbook (8083-15) states that "The float is balanced with a small dip-compensating weight, so it stays relatively level when operating in the middle latitudes of the northern hemisphere. This dip along with this weight causes two very noticable errors: northerly turning error and acceleration error"
My JAA ATPL manuals also talk about N.T.error and acc.error, but they attribute the latter to the mounting of the pivot point being off-centre, thus shifting the CG, rather than having a central pivot point with added off-centre mass; however the result is quite the same.
When it came to all these acronyms; I found that a lot of my students had a hard time with undershoot north, overshoot south. Was it OSUN? UNOS? SUNO? What? So I taught the way I was thinking about the problem during my initial instrument training; in the north pole there are polar bears, which you have to keep away from, so you have to "roll out early". But in the south, like in Mexico, things are very relaxed, and you have plenty of time to roll out late.
