My suggestion would be to use a scale that can be calibrated. This process is also known as "zeroeing out". Get an object that weighs sweventeen pounds, and place the object on the scale. Of course, the scale will dial up seventeen pounds, because the object weighs that much. Find the calibration mechanism, which will allow you to move the weight reading up or down, and move the display down until zero is reached. When you remove the seventeen pound object, the display, if it records in negative numbers, should read -17. This is also called the "tare weight", used in chemistry to negate the weight of the glass containers being used to hold the chemicals used in chemical reactions. Calibration dates back to ancient times, used in marketplaces to insure the buyer was getting the correct amount of goods they were purchasing.