Compare primary and secondary instruments.
Primary instruments
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Secondary instruments
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Gives magnitude of quantity in terms of physical constants of instrument
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Gives reading directly of the quantity measured.
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Need no calibration
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Calibrated with respect to absolute instruments
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Measurement is tedious and time consuming (as indirect) due to calculations needed to be done
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Quick method as direct method of reading.
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Very rarely used.
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Very widely used.
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e.g. tangent galvanometer and current balance galvanometer.
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e.g. magnetic meter, induction meter, hotwire meter and electrostatic meter
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