Tuning at Gillett and Johnston was undertaken according to the 'five toned system, or 'Simpson principle, developed by Cyril Johnston from the writings of Canon Simpson. This was based on the concept that the chord rung by a bell comprised five distinct notes ('strike note, 'hum, 'nominal, 'third, and 'fifth), which had to be harmonised. After the two early rough notebooks (AR1/1/1-2), the main series of tuning books
(AR1/1/3-19) contain details of the tuning of each bell cast or re-cast by the company, including diameter, weight (as cast and as despatched), note, and vibrations (as cast and as tuned). Dates of entries appear to be those of casting rather than tuning, and entries are therefore not in strict chronological order. These books are all marked on the spine 'C.F.J.[ohnston], although they are completed in different hands. All volumes except AR1/1/1 contain indexes of place names.