<p style='text-align: justify;'>GFC Searle's manuscript of 'useful rules', which used to hang in his experimental physics teaching laboratory. ‘Searle’s Class’, as it was universally called, was the practical class taken in 1920s and 30s by undergraduates reading for Part I of the Natural Sciences Tripos. It included a large proportion of students whose primary interest lay in some other subject. (https://doi.org/10.1098/rsbm.1955.0018)</p>