Aggregates must be tested because changes in aggregate properties can cause variations in slump, finishability or pumpability, yield irregularities, or lower than expected strengths. Obtaining a representative sample is crucial to aggregate testing. A random sample taken while aggregate is being moved on a conveyor belt or discharged from a bin will yield the most accurate sample. Basic quality-control and descriptive tests include sieve analysis, specific gravity, unit weight, and moisture content. Quality testing of aggregates requires attention to detail, good equipment, and the mastery of a number of techniques necessary to run the tests.