In reply to Robert Durran:
I’ve in the same camp, had no idea what a romer was. I guess I’ve never spent enough on a compass to have one.
I was once at the Saunders mountain marathon, CP1 was cubic bolder 2m x 3m x 4m (or something similar), clag was down and it was in a boulder field. Dozens of folk were stood at a boulder exactly matching the description and apparently at the right grid ref. It turned out none of us knew how to use a grid ref. We were all stood close to (but very slightly South West of the given 6 fig ref, however it turns out that the given 6 fig ref refers to the SW corner of the 100m x 100m square containing the feature so we were all about 100m SW of the intended feature.
I thought this was fairly poor planning from the route planner, having a feature matching the control description so close to the intended feature however he was completely unapologetic and said that everyone should have a romer and know how to use it.
As a maths teacher this tale does give me an example of when truncation is used rather than rounding, however I still don’t have a romer.