Before revision: It is an older method of measuring frequency, used from the birth of radio in the early 20th century until the development of inexpensive frequency counters in the 1970s, which have greater accuracy .
After revision: It is an older method of measuring frequency, used from the birth of radio in the early 20th century until the development of inexpensive frequency counters which have far greater accuracy, made it largely obsoletewidely1970s, when the .