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Originally Posted by Moneypit SEL
For what it's worth, I've never seen a digital multimeter that wasn't 10Mohm impedance.
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Measurements below 3 Volts frequently involve sensitive circuits which have high output resistance. To measure them accurately, you want a DMM with at least 1000 MegOhms input impedance. Better DMMs automatically provide this high input impedance.
There are DMMs which let the user select the impedance. Some DMM defaults back to 10 MegOhms input impedance, potentially altering the measurement accuracy by orders of magnitude.
Have seen cases where a DMM emits pulses from its measurement terminals, potentially altering your measurement results.
What about this one ? See no impedence listed.
http://www.herbach.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=HAR&Product_Code=A4-221&Category_Code=MM