If you want to trick digital scales you'll need to be able to calibrate them using the wrong half scale and full scale weights. Calibrate with proportionally heavier weights than called for (i.e. 70 & 140 instead of 50 & 100) and the scale will read lower than actual until it's calibrated again.

As for the question of accuracy: while digital scales are generally more accurate than analog scales, scale accuracy can vary widely. Withings smart body composition scales, such as Body+, have been shown to give highly precise measurements of within .

Check the batteries: If the scale is not turning on or showing inaccurate readings, the first thing you should do is check the batteries. Make sure they are inserted correctly and have enough charge. Clean the scale: If the scale is showing inconsistent readings, it may be due to dirt or debris on the sensors.