I mentioned this a while ago as a DIY load cell:
http://www.harborfreight.com/big-game-scale-65613.html

At the time I had only spring scales to check it against. The other
day I found a doctor's office scale for free. It uses weights and
leverage so I trust the accuracy of an old one more than a spring
scale.

Within the HF's 2-Lb resolution a log that weighs 248 Lbs on the
Health-O-Meter shows 248 on the HF scale too.

It wasn't completely free. I spent an hour looking at the gentleman's
fine woodworking projects and fixing his bandsaw.

jsw