What is this instrument?
As the face says, it's a &quot;G meter&quot;, aka &quot;accelerometer&quot;. It measures vertical acceleration in units of &quot;G&quot; (i.e. acceleration due to gravity, 9.8 m/s^2 or 32 f/s^2).
Price would vary, but here's a site with a similar instrument which sold for $75 when it was in stock: https://aeroantique.com/products/accelerometer-g-meter-1?variant=39681371274