Shallenberger Polyphase Integrating Wattmeter (1896) Up
After coming out with his singlephase watthour meter in 1894, O.B. Shallenberger designed a polyphase version. It was just as big and heavy as his singlephase meter (40+ pounds). However, the stators were too close to eachother and interfered with each other with a resulting loss of accuracy.
Shallenberger polyphase wattmeter
GE polyphase metering course pamphlet