Alidade in its real home

Here are some updated photos of Alidade set up in it real home in the Exploratorium Observatory between pier 15 and 17 in San Francisco.  On the left there is an accompanying book which has addition information, current and historical, on the various structures the Alidade can can sight.

 A detail with the point ring (the initials of various structures), bearing gauge,  zone diagram (showing what the zones in the map look like in section) and the map visible.

What you see through the sights, in this case when the bezel was set to Coit Tower. The angular accuracy proved to be very good with the map bearing differing from the actual bearing though the sights by less than a half degree.