Understanding specifications.
Understanding specs"Accuracy, Uncertainty, and Repeatability
Accuracy is often the differentiating specification between similar appearing models. DC accuracy is usually used for the "banner" specification since it is usually better than the accuracy for other functions. DC accuracies of better than ±0.1 percent are just now becoming available. Added to the percentage figure will be a specified number of counts (sometimes referred to as "digits") due to rounding error and noise limitations. For DMMs, accuracy is specified as percent of reading as opposed to percent of full scale as specified for analog multimeters. If possible, avoid use of the bottom ten percent or so of any range since accuracy is badly degraded there. It isn't the percentage error that is the problem; it is the effect of the number of counts deviation becomes substantially larger in proportion to the measured value."
So if the voltage to be measured is 14.8V and the meter meets the stated accuracy of .3 percent then:
14.8V x .003 = .0444 volts. The meter could read anywhere from 14.756 to 14.844, so much for the last three digits!
This paper also gives a good comparison of errors using an average reading meter and true RMS meter.
