USGS reference materials

Every year in the United States, millions
of measurements are made on the chemical
composition of items that affect us on a
daily basis. Determining the accuracy of
these measurements is based on the analysis
of appropriate reference materials whose
composition was previously determined
through rigorous testing. Today, reference
materials help us evaluate the composition
of the food we eat, medicine we use, soil we
grow our crops in, and hundreds of other
products that affect our everyday lives.