This reference data may prove useful for understanding the terminology associated with electrical metering. Included are abbreviations for electrical and metering terms, a shaft reduction (Rs) table, and a chart to be used for comparison of the internal makeup of the various ANSI meter forms.

AC - Alternating Current.
DC - Direct Current.
E - Electromotive force (actually a unit of work). Formulas usually represent voltage with the letter "E" for electromotive force or "V" for voltage.
I - The letter "I" is used in formulas to represent current. You might ask, "Why not use the letter "C" for current or "A" for amperage"? Who knows? As current increases in a conductor, the flow of electrons becomes more intense. Hence, the letter "I" represents the intensity of electron flow.
R - Resistance
L - Inductance
C - Capacitance
Hz - Hertz, formerly called cycles per second.
W - Watts
k - "k" is used as an abbreviation for 1,000 as in kW and kVA.
H - "H" is an abbreviation for hours as in kWH.

Kh - Kh is the meter disk watt-hour constant representing the number of watt-hours per revolution of the disk.
Rr - Rr is the register ratio. This is the relationship between the first take off gear on the meter’s register and the far right hand dial on the front of the register.
Rs - Rs represents the first shaft reduction. This is the relationship between the worm wheel on the disk shaft and the first take off gear on the meter’s register.
Rg - Rg is the relationship between the worm wheel on the disk shaft and the far right hand dial on the meter. It may be calculated by multiplying Rs times Rr.
Kr - The term "Kr" is used to represent the dial multiplier for the meter.
CT - Current Transformer.
VT - Voltage Transformer.
TF - Transformer Factor may be determined from the turns ratio of the CT’s and VT’s. The transformer factor is VT ratio times CT ratio or simply CT ratio if VT’s are not being used.
RF - Rating Factor is the overload factor for current transformers. Exceeding this rating may cause metering inaccuracies as well as risking damage to the CT.
PKh - Primary Kh represents the true disk watt-hour constant for instrument rated meters. PKh may be determined by multiplying Kh times the instrument transformer ratios (TF).
CL - Class rating is the maximum amperage rating of the current coils in the meter. This value is clearly stamped on the nameplate of all modern meters.
TA - Test amp rating. Meters are given a full load test at rated voltage with this value of current. In addition, they are tested with 10% of the TA rating for a light load accuracy test.
W - Number of circuit wires the meter’s stator is designed to meter. The neutral counts as one of the wires. Furthermore, under certain conditions, meters are applied to circuits with more or less circuit wires than stated on the meter’s nameplate.
FM - FM is used as an abbreviation for form as in FM 9S meter.

Shaft reduction (Rs) is the relationship between the worm wheel on the disk shaft and the first take off gear on the meter’s register. Full load RPM (revolutions per minute) refers to the speed of the disk rotation when rated voltage and test amps (TA) are applied.

These diagrams of the basic ANSI standard meter forms show the internal makeup of the most commonly used meters for all AC circuits. Forms 1, 2, 12, 14, 15, 16 are self-contained meters. Forms 3, 4, 5, 6, 8, and 9 are instrument-rated meters. The "S" beside each form number is an indication of a socket rated meter as opposed to an "A" for a bottom connected (A base) meter. The magenta wires are part of the meter socket wiring not internal wiring in the meter.