The surface that your scale is used on should be as level as possible, front to back, and left to right.  While it is more of an issue with balance beam scales even digital scales can be affected.  Balance beam scales usually have an adjustable foot to align the zero mark with an empty scale, but not all allow front to back adjustment which can affect the sensitivity of the scale due to end contact of the knife edge.  If your bench is level enough that bullets aren’t constantly rolling off in random directions you are probably OK.

As with all precision instruments, dust and dirt are their enemies.  Keep your scales covered when not in use and inspect them for dust or dirt under the platform on digitals and in the knife bearing areas for balance beam scales.

The weighing platform of most digital scales can be removed so you can easily clean underneath. A soft artist’s paintbrush or a gentle puff of air is about all that should be needed to clean it. Whatever you do, don't flip your scale over and shake it to dislodge dust and powder grains. Shaking could permanently damage the load cell!  With balance beam scales remove the beam from the cross bearing slot and blow or brush out any dust from the groove and from the knife edges on the pivot.

Don’t forget to clean your powder pan. Over time, a film of powder residue can build up on the powder pan. This can cause powder grains to stick to the pan, and not be transferred to the cartridge case. This is often misinterpreted as static cling and most frequently treated by rubbing the pan with an anti-static clothes drier sheet. Repeated use of drier sheets may also leave residue buildup. Residue buildup happens with both metal and plastic powder pans. The cure is simple. Just wash the powder pan with a drop of liquid dish soap, rinse thoroughly and let dry.  Do not use abrasive soaps or scouring pads. The resulting scratches can cause powder grains to cling. 

Your scale must be on a rock steady platform. A table that moves and shakes will make it impossible to get accurate and consistent readings. If your bench doesn’t have adjustable feet, place shims under the legs to remove any wobble. Remember to protect your scale by taking it off the bench before hammering any shims into place.  Even with a solid bench don't weight things when any other operations are being performed and watch out for appliance induced vibrations in your work area.

Most electronic scales come with a cover. On some of these, the cover isn't just to keep dust off when not in use. Some covers are designed to be used during measurements and  blocking air currents that can affect accuracy. You can some times identify covers that are designed to be closed during measurement as they may have a hole in the top. The hole allows you to add powder with the lid already down. 

Some high end scales come with a “draft ring”, which is usually a glass ring that fits around the weighing pan to protect it from air currents. Make certain it is in place for all measurements.

Balance beam scales are not usually supplied with such shields so it may be necessary to make a homemade enclosure to keep air currents away from the scale. Make it tall enough to extend at least 3 inches above the weighing pan or the beam.

Even if your scale has a draft ring or a cover designed for use during measurements, make sure the scale is located away from air currents in the room.  You may need to put a deflector on the air vent(s) in your room to direct airflow away from where the scale is located. 

Keeping a clear space around you scale.  Static electricity near digital or balance beam scale can affect measurement accuracy just as much as a stray air current.  Always use a powder pan made from metal or from static dissipative plastic . You can also wash you scale's pan with a little dish soap and allowing the soap film to dry on the pan. You can also occasionally wipe the pan with a non-scented frabic softener sheet to achieve the same results.

Keep items made from plastic away from the scale, including plastic or Styrofoam loading blocks, die storage boxes, ammunition storage boxes, Akro bins, etc.  

A weak battery can make a digital powder scale give erroneous readings long before it ever goes dead or gives a low battery warning.   Keep your batteries fresh and buy quality batteries.  Use the manufacturer's recommended battery type and don't replace alkaline batteries with  lithium batteries as the voltages are slightly different (in spite of them frequently being labeled the same).

If your scale has an AC Adapter, use it. It will allow you to leave the scale on for extended periods without worrying about the battery going dead in the middle of a reloading session. Note, however, that most of the inexpensive powder adapters are not “regulated” and their outputs can vary with changes in line voltage.  If your scale is acting strange and you are using the power adapter, try running off batteries (use fresh batteries).

Warm-up time can affect a digital scale's stability. Some scales can take as long as 30 minutes to warm up to a stable internal temperature, especially if the room is unusually cold. With an AC powdered scale, you can just leave it on while you are making other preparations. If your scale has an Auto-Off feature, you may need to disable it or set it for a longer time if possible. Battery powered scales may not allow long warm-up periods especially if it is one that drains batteries quickly.  In that case, allow 30 to 60 seconds warm up time, keep the room temperature as stable as possible before starting a reloading session and use the zero button before every weight measurement.

Check you scale calibration every time you set up for use. Calibration is a good way to tell if your digital scale has warmed up and is ready to use and that there is nothing amiss with your balance beam.. You should also check calibration if the scale has been moved, is being operating at a significantly different temperature than when it was last calibrated, and after you change the battery. If you just bought a new scale, checking the calibration is the first thing you should do before using the scale. 

Perform the calibration procedure as described in the owner’s manual only if the calibration is off.  With digital scales be sure the scale has had a chance to warm up and the readings are stable.  Always use the calibration weight(s) that came with your scale.   

In addition, you might want to keep some objects that you have previously weighed that are lighter and heavier than the supplied calibration weight, or close to powder charge weights you commonly use.  I use a couple of bullets that I have previously weighed on the calibrated scale and handle them only with tweezers.  

You can also use miscellaneous small items like paper clips, coins, and small metal scraps and handle them only with tweezers.  If they don't weigh the recorded amount after calibrating your scale you need to check things out before continuing.

Always zero your digital scale immediately before every measurement, or frequently check the zero point with a balance beam scale.  Some may feel this is overkill, but  it is worth the few extra seconds it takes to ensure the best  accuracy you can get from your scale.

Some digital scales may have a "Tare" button rather than a zero button but its function is the same.

The tare button is used to set the scale to zero with a weight on the pan.

The most basic use as a zero button is to “tare” the weight of your powder pan so the scale reads 0.0 grains with the empty pan in place and the scale will display the weight just the powder charge. It  can also be used for sorting bullets, cartridge cases or even loaded cartridges  by weight by using the following procedure.

1. Press Tare/Zero button to zero the scale.

2. Place the sample bullet on the scale and note the weigh

3. With sample still on the scale, press the tare/zero button  to zero the display and remove the sample

4. Weigh your bullets.  Bullets that weigh the same as the sample will read 0.0 grains.  Bullets that are under or over the sample weight will display the difference in weight. Sort the bullets into weight groups depending on how close you need them to be to the example bullet weight.

Another trick that can be useful.  If you have a sneaking suspicion that you may have double charged or not charged a cartridge, just tare the weight of a known good cartridge and then start weighing the suspect cartridges. All the good cartridges should weight 0.0 grains (or very close too it). So all you need to do is look for one that weighs too much or too little by the weight of the powder charge. This greatly speeds up the inspection process!

If you ever do accidentally overload your digital scale, turn it off and allow to sit for a few minutes.  Then attempt to recalibrate it according to the manual.  If it calibrates check a few known weights of greater or less than the cal weight. If the damage is minor, you may be able to save it.  If it won't calibrate properly you'll have to return it to the manufacturer.

While balance beam scales aren't as susceptible to over-weight damage the knife edge of the pivot can be damaged resulting in a loss of sensitivity and accuracy.  Balance beam scales so damage should be returned to the manufacturer for resetting of the knife edge.

Real men read the manuals for their equipment.  It is amazing what you can learn from them.