Everything To Know About Scale Accuracy
By: Kelly Buck
Here is a question we often get: which scale is more accurate, one that reads 20.0 g or one that reads 20.000 g? Most people would think it is the scale that reads further out, right? The only difference between the scales in the example is that one is setup with a greater readability. The measuring cells, in this case, are identical. Readability is the smallest increment size with which a scale is setup and calibrated for. As a parallel example, a speedometer can be set up with 10 mph divisions, while another speedometer can be set up with 2 mph divisions.
Both of those speedometers have the same accuracy, however one has a greater readability.
Speedometers, like any measuring device, always have some level of inaccuracy. The same is true of scales. All measurements are subject to uncertainty due to a variety of factors. This concept is called measurement uncertaintyand defines the dispersion of values that could reasonably be attributed to the object being measured. Even if a scale company just calibrated your scales, there will be an element of measurement uncertainty in your calculations. Scale manufactures make every effort to minimize measurement uncertainty in their designs. However, there is a always a trade-off between cost and higher accuracy.
Scale companies who understand the importance of measurement uncertainty will ask about your process tolerance and the lightest item that is intended to be weighed on a particular scale or balance. Process tolerance is the range of net weight values that are deemed acceptable. Good weighing practice dictate that overall measurement uncertainty must be less than the process tolerances for an acceptable result.