Recently an American-based German manufacturer was awarded a contract to produce some parts for a Japanese company. According to the contract, critical surface areas of the parts were to meet roughness criteria as defined by the Rz parameter. This appeared to be no problem. However, it turned out that the Rz specified was not the current ISO or U.S. standard version they were used to, but a much older Japanese domestic standard dating from 1982.
One of the differences in Rz evaluation is in the type of filter. The first electrical filters used to separate roughness from waviness data were 2RC high-pass analog filters. These were used until new Phase Correct Gaussian filters (50% G) were introduced in ASME B46.1 in 1995 and in ISO standards in 1996.
Thus, if a part specification is based on a standard written before 50% Gaussian filters were introduced, evaluation should be based on 2RC filtering. In the real world today, many instruments are offering only 50% Gaussian filters for evaluation of all parameters, whenever they were standardized.