How many hours do you think is sensible to take on for demonstrating?? I was thinking one or two practicals a week.

There is a limit, but no one is very open about what this limit is - the most I did in one week was 9 hours, typically 6. I found out later that this was one of the largest totals per semester in the department (I didn't CHOOSE to do all of those hours - I wss just given a timetable at the start of the year, and not knowing that demonstrating is strictly voluntary I just did what I was told).

Yeh I was told today there is a limit, but no one knows how many hours this is. I think 4-6 hours will do me fine. My other work is more important - don't want to let my experiments suffer.