The basic design principles for resistance standards having a resistance differing from the nominal value by less than 0.01% and a phase angle of less than 0.0001 radn at frequencies up to about 20 kc/s are described. The new nickel-chromium-aluminium alloys, on account of their small change of resistance with temperature, appear to be suitable for standards which must be operated with a considerable temperature rise owing to self-heating. Formulae are given for calculating the residual inductance of standards of various types. A one-ohm standard having a calculated phase angle of less than 0.0001 radn at frequencies up to 30 kc/s is described.