Magnetic Locator

Manufactured by the Aqua Survey & Instrument Co. of Cincinnati, Ohio.

An extremely accurate compass, its primary purpose is to act as a metal detector of sorts. The arrow is pointed toward North and the device is held by its strap so that it is just above the surface of the ground. When the tip of the needle appears in the window (via the thoughtful mirror system), you have located metal such as a valve, surveying pin, etc.