Rotary encoder apparatus (2) is described that comprises an encoder scale or ring (30) and an encoder scale reader. The encoder scale includes an incremental scale and one or more reference marks (32,34). The encoder scale reader comprises at least a first readhead (4) and a second readhead (6) that each produce a reference mark signal when passed over a reference mark of the encoder scale. The apparatus also comprises a reference position setter (40) for determining, as the encoder scale reader is rotated relative to the encoder scale, at least one angularly repeatable reference position of the encoder scale relative to the encoder scale reader using a first reference mark signal produced by the first readhead and a second reference mark signal subsequently produced by the second readhead.
