Proper noun
Riefler (plural Rieflers)
A surname.
Invar pendulums were first used in 1898 in the Riefler regulator clock Milham 1945, p.331-332 which achieved accuracy of 15 milliseconds per day. Source: Internet
Milham 1945, p.83 From 1909, US National Bureau of Standards (now NIST ) based the US time standard on Riefler pendulum clocks, accurate to about 10 milliseconds per day. Source: Internet