If the spacing between the two EOG channels is not equal, what should the technologist calibrate?

The appropriate calibration for unequal spacing between the two EOG (electrooculogram) channels is the mechanical baseline. This refers to ensuring that the physical setup of the electrodes is correct, so that they can accurately record the eye movements being studied. When the spacing is uneven, it may lead to discrepancies in the measurement of eye movements, which could affect the data collected during the polysomnography. Therefore, calibrating the mechanical baseline aligns the electrodes properly on the patient's skin, allowing for accurate readings.

In this context, the electrical baseline typically refers to the voltage levels or settings used in the electronic equipment to establish a baseline for the signals being measured, which doesn't directly address physical spacing. The biological baseline generally pertains to the natural physiological signals being recorded and isn't related to the electrode placement itself. The reference channel refers to a standard channel used for comparison in the recording process and is separate from calibrating the EOG channels specifically related to their mechanical positioning.