Horsepower Indicator, -500 to 5000 HP, Allison Engine US Coast Guard and on the B-29 it

and on the B-29 it was installed on the flight engineers instrument panel

Aichi E13A Type Zero Reconnaissance Seaplane aka "Jake"

This is a Carburetor Air Temperature Indicator for a dual engine aircraft as used in the C-46 Curtiss Commando Transport aircraft of the US Army Air Forces during WWII and through the 1950-60's by the US Air Force and civilian operators

and the front page of the Collins sales brochure

Horsepower Indicator, -500 to 5000 HP, Allison Engine US Coast Guard and on the B-29 itThis is a Horsepower Indicator, displaying HP from 500 to 5000 HP at 100% RPM. This was manufactured by Hickock Electrical Instrument Co., part number 560 422, also labeled with an Allison Engine part number 6734355A. Measures 2. 25 inches diameter and ~3 inches deep.