Jerry McCarthy’s day job used to be to write software, in areas such as retail systems, cryptography and internationalisation, for a global computing company. Since his retirement, he now volunteers at The National Museum of Computing (TNMOC), which is situated within the Bletchley Park Campus. There, he talks to visitors about, inter alia, Tunny, Colossus, and the Museum’s slide rule display. He also volunteers at the Instytut Józefa Piłsudskiego, Hammersmith, where he gives the occasional talk on matters cryptological, such as Enigma and early Polish systems for breaking it.