In 1990 ASTM determined that the new style pad with its complete coverage of the weight provided more consistent and reliable results.
Note: if changing from "old style" pads to the "new style" pads, new test procedures may be required as the "new style" pads require more rubs to achieve the same results as the "old style" pads. The reason for this is that the "new style" pads decreases the PSI (pounds per square inch) as the weight is being spread over a larger contact area.
Pads should be changed a minimum of every six (6) months.