The paper is one of a series of five concerning power oscillations between the Central Electricity Generating Board and South of Scotland Electricity Board power systems. It describes techniques and instrumentation used to test power system stabilisers installed on 660 MW generators on the SSEB power system. The stabilisers were installed to improve damping of interarea mode oscillations, which had a characteristic frequency of around 0.5 Hz. The paper describes tests used to prove that the damping of other oscillatory modes (the local mode and intermachine modes) was not degraded by the addition of the stabilisers, and outlines methods used to measure generator and excitation control transfer functions.