If you're interested in buying a laboratory scale, it's likely that there's a bit more at stake than if you were buying a simple bathroom scale. In a laboratory setting, small errors in accuracy can have large consequences, and some of the extra features of a high-end scale -- which would be mere luxuries in a scale meant for everyday use -- can make your life much easier. Here are a few things to help you decide what sort of laboratory scale to buy.
You will find some scales that claim to do it all, to be perfect for every possible laboratory application. Such scales are not necessarily ideal for highly specialized activities, since the manufacturer may have sacrificed the quality of individual features in order to provide a wider range of features. In other words, the old adage — jack of all trades, master of none — applies to scales as well as to people. It may be more expensive to buy a variety of specialized scales for a variety of specialized tasks, but it can save you a good deal of frustration later on.
Possibly the most important specification of a laboratory scale is its readability — which refers not to the clarity with which it displays information, but to the smallest change in weight which it is capable of detecting. Determine how you plan to use the scale and obtain a scale with a commensurate level of readability, whether it be a gram, 0.1 gram, a milligram, or an even smaller amount. Of similar importance is the capacity of the scale, or the maximum amount of weight that it is able to read. A small capacity may be suitable for your purposes, but be sure to take all possibilities into account.
Many scales come with the ability to display information in your choice of units. Among these, some must be configured from a setup menu in order to switch the units, while others are able to switch between units at the push of a button. Of those with push-button conversion, some limit the push-button functionality to only the most common units. Again, it's possible that the small amount of convenience gained by full push-button conversion capabilities won't be worth the extra money you'll pay for such a scale — it all depends on how you'll be using it.
Finally, in a laboratory setting it's often advantageous for your scale to be able to communicate with other devices, such as computers, so that you can easily gather, store, and analyze the data. Some high-end laboratory scales come with serial or USB connectivity. If you already have a device that you're planning to use to collect and analyze the data from your scale, make sure the scale you buy is compatible with the device you'll be using.