A calibrator can either be to a primary or secondary standard. A Primary standard is an instrument that bases measurements on direct, measurable linear dimensions that will not change over time, or be altered by temperature or atmospheric pressure, such as the soap bubble flowmeter range. Secondary standard devices base their calibration upon primary standards & may be affected by temperature, atmospheric changes & mishandling. They can be used to obtain accurate, reliable measurements of pump flow rate if their calibration can be traced to a primary standard & they are handled with reasonable care.

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