Capacity / Readability
Scales come in a wide range of capacities and readabilities. When selecting any measuring device, you should select one which is just as accurate as you need it, but not more. For instance, wristwatches are typically accurate to only a few seconds per year while an atomic clock is accurate to a millionth of a second per day. For daily use, a wristwatch measures time accurately enough to make your appointments on time, but if you had to measure something like the speed of light to several decimal places you would want to use an atomic clock instead. However, the high costs, lengthy setup, and advanced skills required to operate an atomic clock make it out of reach for most measurement processes. Selecting a measuring device that is accurate enough for your application, but not more accurate than you need is crucial. If you purchased a scale with 0.001 g readability when a 0.01 g readability would have been sufficient, you may introduce unnecessary complications such as having to consider more and more influence factors like air currents, vibration, temperature fluctuations, etc.
You should select a scale which has a platform large enough to accomodate all the items you wish to weigh. Expansion trays and containers can help weigh items that are difficult to keep contained on the platform. Scales with larger platforms tend to offer more capacity, but lower precision. The size of the entire scale should also be considered. If you need to travel with the scale frequently, you may consider a portable scale such as a pocket scale, but the platform sizes will be smaller. If you need a scale to use on a countertop, then you may consider a compact bench scale or kitchen scale. For weighing large packages or bulky items, a floor scale is often preferred.