The rate of conversion between pounds and ounces is shown as;
16 ounces = 1 pound
Then you have a digital scale that measures weight in ounces. If you put an object that weighs "exactly 1 pound" on the digital scale, its supposed to display 16 ounces.
However the scale has been described as "not accurate," which implies that the calibration (fine tuning) has been altered either accidentally or on purpose. This also implies that the result would not be 100 percent correct, but it might be a little over or below 16 ounces. Hence the scale might display what in mathematics is termed as "plus or minus" and is denoted by the sign ±
The scale therefore might display 15 ounces or 17 ounces (that is ± 16)
±