The Boyce MotoMeter was patented in 1912, and was used to monitor the temperature of the cooling system and thus the engine itself. These caps were popular from 1912 until the 1930s. They were designed by German immigrant Hermann Schlaich and manufactured in a variety of different sizes and designs, but they all were pretty similar. Originally sold as an aftermarket accessory owners could buy, the manufacturers soon private-labeled them and made them standard equipment.