I recently became aware of the Motometer Central website as a result of my membership of The Society of Automotive Historians. The site is a wealth of information on the Motometer device which became very popular in the 1920’s with the Boyce variety being the most popular. This device is the father of the temperature gauge amongst other modern condition indicators in motor vehicles.

You can find the a history of  Motometers here

You can find information on the Boyce and other Motometers here on Wikipedia

There is a further site Moto Meter Collector here