I have 3 of these available, 2 with the prisms set at: -600 sec., +1200 sec (top to center), and +1800 sec. (top to bottom). The other is set at:-118 sec (bottom to center), +958.9 sec. (top to center), and +1077.5 sec. (top to bottom). The mirror elements are cemented together, so the calibration will stay intact. This unit can be set either horizontally or vertically. They come in their original mahogany box.