Standard minimum values for ammeter and voltmeter readings are taken as 0. When not in use, if the readings show anything else then we can conclude that it has zero error. Zero error is how far from zero, the reading is of the instrument. It can either be positive or negative zero error.
Therefore we see that the zero error in the ammeter is negative zero error while that of the voltmeter is positive zero error.
Hence zero error in ammeter: -4milliAmpere
Zero error in voltmeter: +0.4 milliVolt
So, the final reading as seen is:
Voltmeter: 3.6 V
Now correcting the reading:
Ammeter: [34-(-4)]mA= 38 mA
Voltmeter:[3.6- (+0.4)]V = 3.2 V
Least Count = smallest value measured by a particular measuring instrument (given 0.05V)
Therefore correct reading: Least count × Number of divisions in the instrument
(0.05 × 15)V = 0.075 V (the observed reading of voltmeter)
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