The question says to take the uncertainty in reading the current and voltage for instance, to be the last or fluctuating digit?..what is the last or flutuating digit? what does it mean?

Here is my thought :
For example if you read 12.03 V, they want you to take the uncertainty as 0.01 V. In this case there is no fluctuating digit and the uncertainty is likely the last digit.
While if the lecture of the voltage changes constantly between say 7.89 V and 7.88 V. The fluctuating digit is the last and they want you to take the uncertainty as 0.01V.
The other case (unlikely to happens but who knows?) : The lecture of the voltage changes constantly between 11.7 V and 12.3 V. Even if the lecture varies of 0.6 V, they want you to take the uncertainty as being 1 V. That is, the fluctuating digit.

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Isaac
If the problem is too hard just let the Universe solve it.