Are you letting the scale warm up before using it?
I believe it is suggested to leave for 10mins to warm up before use.
You could always turn it on, zero the pan, then just leave it for an hour or so checking frequently to see how much it drifts.
I've done this with mine and never found it to drift more than 0.1gr, and when it did read .1 it was only briefly.
Bookmarks