Digital Scales - Exorcising the Demons

Plug the scale in, and always keep it on. 
Electronic scales are very different from balance beam scales. Balance beam scales function via a lever on a fulcrum, which when balanced with counterweights at set positions, will give you an indication of how much weight is in the pan. Electronic scales function using a strain gauge. When materials compress or expand, their capacitance changes. A strain gauge takes advantage of this principle and through various electronics, converts that to a digital readout of weight on the scale. As a result, digital scales must be kept "warmed up" at all times in order to give accurate readings. Scales which have only been on for a couple of minutes will not have the electronics in a constant state. Rather, they will be fluctuating slightly based on the electrical current which is allowed to flow through the cool components. Digital scales use almost no electricity, so just plug them in and leave them on indefinitely. If you are unable to do this for some reason, just get into a good regimen where you let them warm up for at least a few hours before you rely on their readings. Obviously scales of very high pedigree will require less warm-up time than cheaper scales, however this rule seems to work well when applied to all digital scales of any quality.

Use a battery backup with power conditioning
AC current can be unreliable in rural areas and is often "dirty power" even in the best grids. In keeping with the first guideline above, you should use an uninterruptible power supply, otherwise known as a battery backup. This battery backup should also have a power conditioning feature so that it not only keeps the scales powered on at all times, but filters out the noise and fluctuations in that power. You won't need a very large unit. As I said above, powder scales use a minuscule amount of power. A good 100watt power conditioning battery backup will typically cost less than $100.

Avoid electromagnetic fields
The most common source of electromagnetic fields near the reloading bench is fluorescent lighting. The light bulbs themselves do not emit much of a field, but the ballasts in the fixtures themselves emit a ton of interference. Especially the cheap hanging shop light variety often hung above loading benches. This effect can be minimized by using light fixtures with digital ballasts, or avoiding fluorescent lighting all together. Low power consumption light sources such as LED's is definitely the way to go here. Lots of light, with low noise signature. Another common source which is becoming less common every day is CRT monitors. These come in the form of old televisions or old computer monitors. They produce even more massive magnetic fields than the fluorescent light ballasts.

All vibrations are bad vibrations
The strain gauges and other electronics inside digital scales are very sensitive. Do not subject the scale to constant wiggling such as that caused by a reloading press ram being run up and down thousands of times. Isolate the scale using a soft rubber or neoprene pad beneath the scale and your bench. This can be found in the form of a cheap mouse pad. Make sure it is the dense soft rubbery type, rather than the super light and relatively stiff foam type.

Kill the static electricity
Of all the demons that vex consumer-grade digital scales, static electricity is probably the one that haunts most frequently. This is largely because they are comprised of plastic components and housings. Not terribly convenient, but relatively simple to solve. Get yourself a box of dryer sheets to keep in your reloading room, or raid your wife's laundry room. Wipe down all the exposed surfaces of your scale from time to time to ensure no static charges build up on it. Wipe down any other plastic objects near the scale as well.

Calibrate, calibrate, calibrate.
Depending on how well all of these guidelines are followed, and what quality the scale is, calibration may need to be done frequently. Each scale requires different procedures to calibrate, but there are some constants I can share with you. First, when calibrating you must be mindful to time how long you let each calibration weight set on the pan before moving to the next step. Calibration is usually done toward the outer limits of the capacity of the scale. As a result, the calibration weights will not instantly show the correct weight when placed on the scale. The longer you leave them on there, the heavier weight they will show. This might require some trial and error, and stop watch will go a long way to helping you get it right. Use the calibration weights to check your setting afterward to ensure you are right on. If you aren't, you might need to modify your calibration technique.

Be sure to check your scale for drifting periodically. New scales should be checked very frequently, as in every 10-20 rounds at minimum. I watch all new equipment closely until it has proven itself, but scales should be watched extra close considering they can result in you being seriously injured if a weight is off by too much. If you find yourself having to calibrate too frequently as a result of your scale drifting often, you'll want to replace your scale. It simply isn't worth your time to work with a finicky scale.

Keep cell phones and radio's away from your scale.

Radio frequencies can interfere with digital scales a great deal. Cell phones, radio's, and wireless computer equipment all fall into this category. Basically anything that transmits via RF or microwave of any kind. I've talked to many people about their malfunctioning scales, only to find they had their cell phone laying on the bench right next to their scale. Remove the phone from the room, and magically the problems disappeared. Wireless routers or wireless cards in your computer can cause the same interference. Keep all other electronics a good distance away from your scale. There are various meters you can buy which detect RF and electromagnetic fields if you want to take a scientific approach to seeing how much noise is in your reloading room.

Control the air. 
We want scales that are very precise to measure our powder charges. This sensitivity to weight can cause complications if you are in an area of high air flow. Heating/cooling vents, windows, drafts, someone walking through the room, or even your own breath are enough to completely invalidate the weight displayed on that scale. Keep the space around your scale completely void of air movement for the best success.

Keep the pan empty.
Leaving a charge on the pan for extended periods of time can cause the electronics to "take a set." Scales are designed to be empty unless they are taking a reading. The strain gauges can have a bit of "memory" if you leave weight on them for too long. Sometimes they will come out of it, while other times they will be permanently damaged. Keep the pan empty and clean.

Ensure amount of powder in dispenser does not cause drifting.
Some scales are offered as a pair with a powder dispenser, such as the RCBS Chargemaster 1500 combo. Some combination units can exhibit drift depending upon the amount of powder in the silo of the dispenser. Be sure to test your scale a few times when it is new to ensure that it does not produce different readings on a full silo as compared to an empty silo.

Control your climate. 
Many people do not have their reloading benches in the best of places. They often have them in the garage or humid basement which is not optimal for maximum consistency. Digital scales are very sensitive to temperature, as we previously established, so the ambient temperature in the room should be the same from session to session as well. If you load in 80 degrees and 90% humidity one day, and 70 degrees with 20% humidity the next, you can count on your scale drifting quite a lot between those two sessions.

Get on the level. 
Making sure your scale is level is just as important for digital scales as it is for balance beam scales. Ensure all the feet are making contact and that those feet are handing the weight equally. Sometimes it is best to build a separate platform to support the scale if you can not get a nice flat surface to level the feet on.

Place objects and charges consistently. 
Consistency in how you place your charges in the pan is key to getting precise readings. If the powder is stacked up against one side of the pan, it can put uneven stress on the strain gauge and result in bad numbers. This should be considered when you are calibrating as well. Calibration weights placed haphazardly will result in inconsistent calibration.

Don't slap it around. 
Sharp impacts can damage the sensitive electronics in these scales quite easily. Most high end scales will ship with an anchor in place to ensure they aren't damaged during shipping. Once setup, it is important to shield your scale against impacts. Do not be handling bullet boxes, dies, or other heavy things around your scales. One hit can be all it takes to turn your several hundred dollar digital scale into a paper weight.

Do not overload the pan. 
One sure way of destroying your scale is to put more weight in the pan than it is rated to read. The strain gauges are not limitless in their abilities. Your scale will have a specification sheet which will tell you its maximum payload. Be sure to stay within that envelope and you shouldn't have an issue. Most scales will be permanently damaged if you overload them.

Avoid battery powered scales. 
Battery powered scales are almost always far less reliable than AC powered scales. This is obviously due to the fluctuating power provided by batteries. If you are loading where you do not have power, stick to balance beam scales as they will prove more accurate than most consumer-grade battery powered digital scales. There are some very expensive laboratory-grade scales which have proven to work well if you are set on a digital however.