Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 148,151 pages of information and 233,681 images on early companies, their products and the people who designed and built them.
Signalling Equipment Limited or SEL of Merit House, Potters Bar, Middx. Telephone: Potters Bar 2262-3. Cables: "Sel. Potters Bar"
1943 June. Advert in Flight magazine for Morse Complete Practice Unit. 
1947 Listed Exhibitor - British Industries Fair. Manufacturers of 4/6 V Motors, Transformers, Electrical Outfits, Model Dynamos, Induction Coils, Miniature Electrical Equipment, Microscopes, Magnetic Compasses, Telescopes, Theatre Glasses, Model Stationary Steam Engines, Morse Practice Keys and Buzzers. (Olympia, 3rd Floor, Stand No. K.2420)