In what year did Shure begin to replace CPS (Cycles Per Second) with Hz (Hertz?)
The year was 1964.
The technical measurement term "Hertz" was established by the International Electrotechnical Commission in 1930. It was adopted by the General Conference on Weights and Measures in 1960, replacing the previous name for the unit, cycles per second (cps.)
Brief Biography of Heinrich Hertz