2 ms·

This device pre-dates the Zone system by quite some time.

• lmilcin 5y ago
  Actually, I could not find a date. Adams was born in 1902 and Kaufmann in 1885. Zone System was "formulated" in 1930 when Kaufmann would have been 45. Kaufmann was said to be quite brilliant at early age and so it is possible or even likely that the device predates Zone System, but not by all that much (probably 2 decades at most).