The pendulum hardness test is based on the principle that the amplitude of
the pendulum’s oscillation will decrease more quickly when supported on a softer surface.
These instruments meet the requirements of ISO 1522, ASTM 4366, DIN 53157, and BS 3900: E8.
 
The Persoz test measures the time taken for the amplitude to decrease from
12° to 4°. The Koënig measures time taken from 6° to 3°.
 
The times taken in Persoz tests are approximately double those in Koënig tests and
so the Persoz has a greater degree of discrimination. The Persoz does, however,
tend to skid on harder surfaces.