Once again - someone has to explain to me how using check weights is going to solve the problem Balrog is having with a wide swing in weight readings of his powder. Check weights are an excellent accessory to have, but they don't solve this particular problem.
OK, the check weights will determine if your scale is accurate. Or needs calibration. Then you know when dumping powder on the scale pan that it's measuring the weight of the powder correctly.
I have been using a RCBS powder pro for 14 years,(made for them by pact). It has only failed me once, it needed to be re-booted. A call to pact gave me instructions on how to do that, I was calling for shipping instructions.
It is paired with the pact dispenser. But mostly I use it for weighing bullets, and setting measures.
I have the smaller set of check weights from Lyman;
http://www.midwayusa.com/viewProduct/?productNumber=212586
They come in the following increments;
Check weight set includes:
# Two 20 grain
# One 10 grain
# One 5 grain
# Two 2 grain
# One 1 grain
# One 1/2 grain
For a total of 60-½ grains. That pretty well covers all non-magnum powder charges.
Another thread recently, one person who was a lab tech. said these weren't all that precise. But on my pact/RCBS scale they always weigh what they're supposed to. If they don't, then it's time to calibrate.
Another thing that most don't bother with, or just plain don't know. The surface your scale sits on must be
LEVEL. No bones about it! Level in one direction, then at 90 degrees, not just level one way.
Take a carpenters level to see if your bench is level. If it is not, then you will have to either level the whole table, or provide a stiff level surface for the scale to sit on. Unless you have some weird iron rock formations underground, gravity runs at exactly 90 degrees straight up. If the scale is tilted off center, you've induced an angle into the equation.