if the scale is varying a lot, then you need to look over your setup. I use a Pact with virtually zero drift (actually three of them). No digital scale likes air drafts and some folks complaign about flourescent lights (I've not seen that problem). A ground fault loop will also cause you havoc, but is also easy to cure. All scales want to be level (analog or digital), and most scales don't like vibration (analog or digital)
I bought a LYMAN and glad I did. I use a trickler when loading only for accuracy.
I recheck every 5th load and it always stays the same. don't do a lot of heavy breathing, keep it leavle, let it warm up and just to know how accurate it realy is drop a hair on the tray.