This may be of interest to someone wanting to display/measure accurate voltage and current at the same time. This tracks my Fluke 187 by .01 in volts and within 30ma in current. The meter can be driven from source or external. I use 12vdc wall wart for low voltage use and found accuracy the same over x-former or clean DC supply. This unit can be calibrated by user but I had to search online for the procedures as no documentation came with meter.