St Johnston
In 1953, St Johnston left the British Non-Ferrous Metals Research Association and joined Borehamwood Laboratories of Elliott Brothers (London) Ltd, where she worked in the Theory Division. The company was an early computer company and had produced its first computer in 1950. St Johnston learned to programme at the company and also at the 1954 Cambridge Summer School on Programming and, showing a real flair for programming, began working on EDSAC and the Elliott 400 and 800 series computers. By 1954, St Johnston was responsible for the programming of the Elliott 153 Direction Finding (DF) digital computer for the Admiralty and soon after for programming Elliott's own payroll computer; her work was said to have been inventive and structured, but also very accurate, hardly ever requiring ‘de-bugging’.