This handbook contains in a compact and easy-to read form, the principles governing conventions for electric and magnetic circuits (IEC Publication 375) and the standardization of letter symbols together with a list of letter symbols in general use which have been approved prior to the date of printing of this handbook (IEC Publications 27-1, 27-1A, 27-2, 27-2A, 27-2B and 27-3). The list of letter symbols gives the name of the quantity in English and French as well as Dutch, followed by the symbol for the quantity and the appropriate SI unit with its symbol, which are the same in all languages, thus indicating the universality of letter symbols and units.