At Last I have found the perfect compass! I already had a variety of compasses but all suffered from a fundamental fault: Changing radius midway though drawing an arc.
I have lost count of the number of students who tell me “I’m hopeless at using a compass”. I have come to the conclusion they have been using rubbish compasses!
The Faber-Castell Grip compass isn’t cheap at around £20+P&P but it is really nice to use something that draws perfect arcs, lovely circles, and is really easy to get a good result with.