Allan, There is the alternative of stellar observation, i.e., Polaris, and the other circumpolar visual stars. A fairly simple setup of fixed concentric-rings or a pin bar as fore-sight, and an adjustable position rear-sight should, over a couple of nights of converging approximations, serve for dial-setting to a few minutes of arc. (The sighting system would be clamped and looked through in reverse to place references on the ground.)
Bill Maddux
