It was the '80s so safety razor blades were available but in a posh public school (UK version) aged ~17, compasses were everywhere and large old style razor bla

It was the '80s so safety razor blades were available but in a posh public school (UK version) aged ~17, compasses were everywhere and large old style razor blades were not - the modern style razor with one or two thin blades was a thing. We could have probably got some needles from matron for a finer point, than a compass. Your pair of razor blades is a great solution.