NavList:

I will modify my original response to Bill a little. It seems to have inputs that will determine the direction of a meridian, rather like the more familiar astro-compass. Though the latter is more concerned with direction, it in principle does so by measuring from a N - S line. The mirrors I suspect are for aligning the instrument, held on some sort of knife edges, over a survey point, though is is also possible that it was someone's elaborate attempt at producing an instrument for gyro compass correction,but precision to the degree implied by the micrometer drums seems to be excessive.

Bill Morris

Pukenui

New Zealand