for determining amount of fuel.
Instruments for Navy and Army machines are of course more complete. In the specifications for Army Hydroaeroplanes (twin motor type 1916) the following instruments are specified:
Aneroid Barometer.
Graduated in feet, and reading from sea-level to 12,000 feet.
One in each cockpit. To be of the Sperry Gyroscopic type with an elastic suspension and properly damped. Shall be attached to, and synchronized with, the ground drift indicator.
Located in observer's cockpit. For noting drift due to side winds. See illustration on page 244.
Special aeroplane type, built to resist vibration. Located in pilot's cockpit.
Fig. 14. Aeroplane Compass of the McCreagh-Osborn Type. (Sperry)
To indicate the amount of fuel in gravity service tank at all attitudes of flight, and shall be visible from pilot's seat. A gage in the main tank will also be desirable that will register the approaching exhaustion of fuel. This indicator should register when 75% of the fuel in the main tank is exhausted, and then record the remainder continuously.