Workhorse

Despite spending quite a lot of my life doing "big hard sums", I've only ever owned two calculators.

The first one, an earlier model of the above, lasted from the start of Standard/ O Grades until just after my finals, after which it gave up the ghost. This one has lasted a doctorate and the subsequent 12 years. Unlike the calculators of most of my students, it can't sketch graphs. Unlike most of my students, with a following wind, I can still sketch a graph.

PS It is bad luck to clean a calculator. It weakens the counting mice who live inside.