  It has recently been pointed out by Finn that the long-standing derivation of
the response of an interferometric gravitational wave detector contains several
errors. Here I point out that a contemporaneous derivation of the gravitational
wave response for spacecraft doppler tracking and pulsar timing avoids these
pitfalls, and when adapted to describe interferometers, recovers a simplified
version of Finn's derivation. This simplified derivation may be useful for
pedagogical purposes.
