About a few milliseconds later the horizontal IR diodes will pulse and the vertical detector diodes measure vertical eye position. The recording resolution for the 12 bit signals is one part in 4096. Of course the biological stability of the eye is not that small. The goggles themselves and the associated circuitry have very little drift. This can be demonstrated by placing the goggles on the table, and covering them with a cloth to block ambient light.
Measured traces show no significant drift.
The goggle card circuitry is DC and is affected by semiconductor thermal sensitivity. We have found that the drift can be significantly reduced by placing a conducting silver paint coating over the clear molded plastic over the inside of the goggle printed circuit cards. Of course, small optical windows are left for the pulsed IR diodes, and the photo-detectors. The drift is reduced because the silver paint coating shorts out the temperature gradients in the circuit card, and because of the IR reflection by the silver coating. This feature is not recommended for NMR application because conducting material can affect the pulsed RF fields.