By the mid to late 19th century, efforts were being made to standardize electrical measurement. Lord Kelvin was an important figure in this process, introducing accurate methods and apparatus for measuring electricity. In 1857, he introduced a series of effective instruments, including the quadrant electrometer, which cover the entire field of electrostatic measurement. He invented the current balance, also known as the "Kelvin balance" or "Ampere balance" ("SiC"), for the precise specification of the ampere, the standard unit of electric current.