There are multiple ways of expressing the accuracy or precision of an instrument or test method. The most common method in our industry is to measure on traceable standards in a calibration laboratory. This is challenging for surface profile measurement instruments because no traceable surface profile standards exist. For some instruments, such as depth micrometers (ASTM D4417 Method B), accuracy can be estimated using calibrated height standards. For replica tape, the ASTM D01.46 committee used a set of panels blasted with a range of surface profiles, and compared the results from replica tape against measurements taken on the same panels using a calibrated drag stylus micrometer (ASTM D4417 Method D). Across the 0.8-4.5 mil (20-115 micron) primary range of replica tape, the readings differed by less than ± 0.3 mils (± 9 microns), as summarized in the table below.
However, this tests the accuracy of the instrument or apparatus, but not necessarily the overall test method. For most users, it is more important that measurements are consistent between the various parties (for example, the specifier or contract author, the contractor, and the inspector). Because blasted surfaces are complex, random shapes, the ability of an instrument to measure height in a laboratory is not necessarily indicative of its ability to measure surface profile in a consistent, repeatable manner in the field.
In 2011 the ASTM D01.46 committee preformed an interlaboratory study, which measured the reproducibility of measurements made by multiple users and laboratories (stated as the range that 95% of measurements from all operators across all laboratories fall within). The results are summarized as follows:
The accuracy/reproducibility values are specified at 3 mils in the above table, and typically vary across the range of an instrument. For Replica Tape:
In summary, independent studies have shown that Testex Press-O-Film replica tape is a highly accurate measurement method with industry-leading reproducibility.