Digital scales are a hot topic on every reloading forum you go to. Guys love them and hate them. Beam scales aren't infallible, but they aren't affected by some of the things that can affect digital scales. Digital scales can be effected by battery vs AC adapter use because the adapters have to step the voltage from 120 down to 5 to 9 volts and change it from AC to DC. This process leaves a DC voltage that isn't as clean as battery can provide, especially if the adapter is cheaply made. Also, the adapters can be affected by voltage fluctuations. Very few power companies provide AC at a steady 120 volt average, and the adapter has to be able handle these fluctuations too. And you can't get a cheap electronic scale without a cheap adapter. The electronics in an electronic scale can also be affected by outside electric/magnetic fields, such as those created by the ballasts in fluorescent lighting fixtures. Again, this shows up more in cheap scales, but some higher priced can be affected too. Another problem area with electronic scales are how the scale's platform is mounted in conjunction to the electrical components used to measure and determine the weight. For example, the Dillon scale I have has four plastic posts that are used to transfer the weight from the platform to the inside of the scale. Moving a weight around on the platform will change the weight reading. One last item that will effect an electronic scale is air currents, even those created by the reloader him/herself moving. Because of magnetic dampening, beam scales are less susceptible to these currents.
If all this sounds like I dislike digital scales, let me say I don't. By understanding what can cause them to have problems, you can mitigate those problems. Eliminating the first few problems should be pretty obvious: avoid cheap scales. I've found the same advice holds true in other cheap digital products such as digital micrometers or the popular calibers. These aforementioned products may be close enough for some purposes, such as determining a bolt diameter, but for close work, quality pays, it doesn't cost. That's especially true when we're talking about powder charges. Consistency is a key when using any scale, and electronic units can especially benefit from this. Make sure the scale is level. Avoid placing it anywhere there are vibrations, like next to your press, or air currents, like near a ventilation duct. Again, beam scales are magnetically dampened, so these vibrations and currents will have less effect on them. Check the scale before use with a weight that is as close to the weight you plan to measure. RCBS makes a set of weights that are handy for this. And place charges consistently on the same place of the scale's platform each time. Following these tips will help ensure accuracy of any scale, but are more important for electronic than beam units.
