Digital computer models of a selection of 2-input phaseand amplitude-comparator distance relays, generating mho and offset-mho characteristics in the steady state, are described and evaluated under transient conditions, necessitating interpretation of the criteria of operation in instantaneous terms. The primary system is simply represented by sinusoidal-voltage source and lumped impedances, comparator representation includes consideration of finite sensitivity and the provision of self polarisation. Dynamic performance is presented in the form of contoured distance-to-fault/system-impedance-ratio curves.