Abstract: The percent error in the value of a resistor, relative to a nominal value (R.sub.n) of the resistor is determined automatically with a Wheatstone bridge having first and second branches energized by a voltage source. The first branch includes first and second series connected resistors respectively having values P and Q. The second branch includes third and fourth series connected resistors respectively having values R and A; the third resistor is the resistor being measured for percent error. The fourth resistor has a value to establish bridge balance when R = R.sub.n. A diagonal is connected across a common terminal of the first and second resistors and a common terminal of the third and fourth resistors. A voltage source driving the two branches in parallel has a value in accordance with: ##EQU1## WHERE: K = P/Q and is much less than 1,u = the voltage across the diagonal that is directly proportional to the percent error, andm = an integer.