Measurement and Instrumentation
The measurment of very low and very high frequencies is invariably done using a frequency counter in which one of the following?

 Frequency measurment modes only.
 Period measurment modes only.
  Period and frequency measurement modes respectively.
 Frequency and period measurment modes, respectively.

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Measurement and Instrumentation
The measurement of a quantity

 is a comparison of an unknown quantity with another quantity.
 is a comparison of an unknown quantity with known quantity.
  is a comparison of an unknown quantity with standard.
 none of these.

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