Ron,
I have done a number of tests on the digital scales your talking about, sorry to say, I didn't find them up to the job.
Found the fox scales read OK, IF you had a new battery in them every time, if not the scales gave the wrong reading.
Idid the test against a set of Avon's and heatons that had both been Calibrated, and showed to be weighing correct.
Shame that the Avons are not made any more.