Originally Posted by Retro Grouch

You're basically right, but sometimes there's a catch.

The top part of the saddle lamp floats and adjusts itself to the bottom. It's possible to loosen the top part of the clamp, adjust the seat and, when you tighten it back, the seat angle returns to exactly where it was before.

The bottom, serrated portion of the clamp sometimes gets stuck on the fixed portion of the seatpost. When you adjust the seat angle it's important to be sure that the bottom portion has been knocked clear so that it can be readjusted to the angle that you want.