from "Hand book of Electricity Metering" ninth edition. quoted from text on page 136.
Kh is the number of watthours represented by one revolution of the disc.
Rg The necessary gearing is provided so that the revolutions of the disc will move the first (or right-side) pointer or cylinder one full revolution (360degrees) each time the rotor revolves the number of times equal to ten kilowatt-hours of usage. This is known as gear ratio, or Rg.
Rr The register ratio, known as Rr is the number of revolutions of the wheel which meshes with the pinion or worm on the disc shaft for one revolution of the first dial pointer.
