Metrication in the United States There are no U.S. customary units for electric current, potential difference, or charge since these concepts were developed after the international adoption of metric in science. The metric units ampere, volt, ohm and coulomb are the only units used. The SI term hertz has replaced the term "cycles per second" as a unit of frequency. Energy is often measured in watt hours, BTUs, therms or calories rather than the SI joule. Residential and commercial electrical energy use is metered and billed in kilowatt hours, kW·h, as in most metric countries. Force measurements regularly use the pound instead of the SI
Thymidine kinase 1 of malignancy, furthermore, TK-1 has been found to be elevated in serum even before clinical symptoms appear. This offers the potential for earlier therapy. Elevations in serum TK-1 have been found to correlate with the return of breast and other forms of cancer TK-1 can be used to detect cancer earlier, determine what stage it is in, and detect recurrence. Thymidine Kinase 1 can be measured based on its enzyme activity or using immunoassay. Thymidine kinase 1 Thymidine kinase 1, soluble (gene name TK1), is a human thymidine kinase. Two forms of this protein have been identified in animal cells,