The traditional analog wattmeter is an electrodynamic instrument. A directional wattmeter indicates forward power, reflected power, and often SWR as well. Therefore, a wattmeter is rated not only in watts, but also in volts and amperes. A modern digital wattmeter samples the voltage and current thousands of times a second. In 1974 Maghar S. ChanaRamond L. KraleyEric A. HauptmannBarry and M. Pressman patent Electronic wattmeter. The patent was granted for the Directional Wattmeter in 1958. He also invented another Wattmeter, the eponymous " '' ". This maximum iron loss is measured using the wattmeter. The two circuits of a wattmeter can be damaged by excessive current. The Bird Model 43 Thruline Wattmeter was created in the early 1950s. A wattmeter is connected to the primary. Thus the wattmeter measures only the iron loss. See Wattmeter for an alternative use for this instrument. A wattmeter is used to measure electrical power.