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If you are really looking for an accurate meter, get a really cheap digital meter for a few $ or £ plus a "Precision Voltage Reference Source, 5.000 volts, 0.02% accuracy" ... I have just sent for one of these at a cost of $14-55 (£9-44) plus postage to the UK (off Ebay) ... All you need to do is check what your cheap meter reads for the reference voltage and that will show you how far off your meter is at five volts ... This means that you can accurately correct the 4.2 volt cell reading to within 0.02% or better ... So this device is at least 40 times more accurate than the meter ... You won't get better accuracy anywhere for any sensible price ... I use a Maplins £4 or £5 meter which has an accuracy of 0.8% on the 20 volt range (0.5% on the one volt range) ... A similar model is available in the US for about half this price.
The 5.00 volt Reference will work on any meter ... I will check my meter every month or so just to be certain that the cheap meter is still OK ... This is still a more accurate method than relying on a mega-expensive meter alone ... You might have friends in electronics who could build you one cheaper ... I considered that, but this one comes with a statement of how far it is away from 5.000 volts, so it can give you an absolute value better than 0.02% ... That is good enough for most people.
You could use your Radio Shack meter having checked it against a reference and corrected the reading as necessary ... No need for a mega-expensive meter when you have a much more accurate reference.
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