“Precision” consists of repeatability by one person within one laboratory and “reproducibility” between multiple laboratories. Tables 1 and 2 below show repeatability (r) and reproducibility (R) data from the C 1028 method for five different materials chosen
for precision testing by the ASTM committee in charge of this test. Table 1 is for dry tests, Table 2 for wet tests. (Click on the tables below to see them in pdf format.)
The repeatability limit r for dry testing has a maximum of 0.0678, which rounds off to 0.07. This indicates that if the same operator in the same laboratory tests the same material twice on the same day using the same equipment and gets SCOF results of 0.53 and 0.60 — a difference of 0.07 — this is considered within the normal variation for this test method. Either result, 0.53 or 0.60, is equally correct.
The reproducibility limit R for dry testing has a maximum of 0.1392, which rounds off to 0.14. This indicates that if two operators in two laboratories using different equipment test the same material dry and get results of 0.46 and 0.60, this is considered normal variation from this test method. Again, either result, 0.46 or 0.60, is equally “correct.”
For wet testing the repeatability limit r within one lab is as high as 0.0617 (or 0.06), and the reproducibility limit R between laboratories is as high as 0.10. (These maximum numbers could easily have turned out to be higher had more than five tiles been tested.)
One should therefore pay little attention to moderately large differences (like 0.07 or 0.14) in any test results obtained using this method.
The ASTM committee that approved this method affirmed, repeatedly and unanimously or near-unanimously, that this method is not intended
to assess slip safety.