Vintage Aircraft Pyrometer, ELECTRIC THERMOMETER FIELD TESTER N-3A, 

Manufactured by Lewis Engineering Co, US,

Spec Mil - T - 7449 C 

Dated around 1960's

Manufacturers patent number PT No 81T27

The item originated from a old UK US Air Force Base.

The case is made from solid brass or copper, so has a high value, just as it stands !

Appears complete and potentially in working order, but untested.

Good used condition, with some wear, marks, scratches and paint loss.

The another reference to such an item, but looks older !https://www.ebay.com/itm/THE-ROFLAN-CO-TYPE-N-3A-ELECTRIC-THERMOMETER-FIELD-TESTER-STOCK-R4920-620-3-/184426435416

46cm wide, 27cm deep, 16cm high

Very expensive item originally !

The temperature of numerous items must be known for an aircraft to be operated properly. Engine oil, carburetor mixture, inlet air, free air, engine cylinder heads, heater ducts, and exhaust gas temperature of turbine engines are all items requiring temperature monitoring. Many other temperatures must also be known. Different types of thermometers are used to collect and present temperature information.