2.VerbTo change (a number) to an approximation having fewer significant digits."The instructions say that we are not to round off until we reach the final figure. [in a calculation with interim steps]; Round off 15.4 to 15, round off 15.51 to 15.5 or to 16, round off 0.499 to 0, and round off 970,000 to 1 million.; "This product contains no PCBs" is a typical commercial distortion if it actually contains 0.498 of the measurement unit, rounded off to "0""