- GeoRef, Copyright 2008, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
The average aperture size of a sieve may vary 0.08 phi-unit from the stated aperture size because of manufacturing tolerances. For sediment studies requiring greater than routine precision this possible error can be eliminated by calibrating the sieves with samples of glass spheres especially prepared for sieve calibration by the National Bureau of Standards. The routine particle size analysis of sediments, however, does not require the use of calibrated sieves.