The paper reviews existing theories of the oscillating-disk viscometer and demonstrates their inadequacy. Using the results obtained previously by Kestin and Persen together with an empirical assumption that the edge-correction factor is proportional to the ideal viscous torque pieced together from the infinite-disk and infinite-cylinder solutions, the authors are able to develop working formulas which, in addition to the edge effect, include the effect of wire damping and unequal separation. The effect of a stem is discussed separately and shown to be negligible. Some remarks are made about the decrement-period relationship. The assumptions are compared with experimental results which demonstrate that for a given suspension system the edge-correction factor C depends on the dimensionless ratio x0 = δ/R (δ = √[ν/ω0] is the average boundary-layer thickness and R is the external radius of the disk) in a unique way. This shows that the use of the authors’ equations together with a suitable calibration procedure should lead to reliable values of viscosity.