Abstract: A wrist-worn electronic device comprises a housing including a bottom wall configured to contact a user's wrist, an optical transmitter and receiver assembly and a processor. The optical transmitter and receiver assembly comprises a first optical transmitter array, a first optical receiver, a second optical transmitter array, and a second optical receiver. The first and second optical transmitter arrays transmit a plurality of first and second optical signals, respectively, that pass through a user's skin. The first and second optical receivers receive the first and second optical signals that travel along a first signal path and a second signal path, respectively, that are both substantially parallel to an arm axis of the user. The processor is configured determine physiological information about the user based on one or both of first and second electronic signals corresponding to the first and second optical signals.