Astronomical Calculations

Exploration Stage: Observatory
From: Detective
Description: There are many suspicious devices here. I think the people who lived here were making their calculations using an Ancient Calculator. So, which of the gadgets scattered around the Observatory fits the description of a calculator? Will you help me find it?
Completed: Buddy, are you sure this is an Ancient Calculator? I would never have thought that this was a calculating machine. Our mystery woman is very smart if she knows how to use this.