Uncertainty in resistance measurements with multimeter

[Tom Pietress]

I am writing a report on an experiment involving measuring the resistance of one component with different multimeters, and finding the uncertainties of these measurements from the multimeters themselves. For example, with one of the multimeters I got 270.1 ohms. This multimeter have stated "0.7% + 1D" which means the uncertainty is +/- http://www.vissarion.biz/div/untitled.JPG ,[/URL] the square root of 0.7% of the measured value squared plus the last significant digit squared.

However, one of the multimeters have specified "0.05% + 2D + 0.02 ohms".
I assume that 0.02 squared should be added to the equation, but what does 2D mean? Is it the last significant digit times two, or the last two significant digits? I assumed the latter, using 0.1 squared (since there are two significant decimals in the measured value), however this gives an uncertainty so very much smaller than the others. One of the goals is to establish a value that exists in all of the measured values +/- uncertainty, however the value I get here does not overlap the other values.

 

[berkeman]

for 0.7% + 1D, I think you need to multiply the actual resistance by +/-0.7%, and then add/subtract a single digit increment in the least significant displayed digit.

for 0.05% + 2D + 0.02 Ohms, you multiply the actual resistance by +/-0.05%, add 0.02 Ohms, and add/subtract two increments of the least significant displayed digit.

I'm no expert on this, but that's how I would interpret it. Is there any more information at the DVM manufacturer's websites? Like check out Fluke's website, for example.