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Why are sample
results often reported as “less than” some number rather than
“0”?
Sample results are
often shown as “< 5.0 mg/l” — read as “less than five
milligrams per liter.” This is because the test method or test
instrument (in this case, looking for the number of milligrams in each
liter of sample) begins to detect the amount of a substance at some
particular level that is more than zero. As test methods and test
instruments evolve, they can detect substances at lower and lower
levels. Thus, “< 5.0 mg/l” means that the substance was not
detected but it might be present at some amount that is too small to
detect.
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