Danny,
Just like Bird, I finally got around to checking on some threads that I haven't had time to look at, and that's when I found this one./w3tcompact/icons/smile.gif
Your fish scale will probably work just fine. I use a similar kind of scale to test the amount of pull it takes to open the doors in our municipal buildings to meet ADA regulations. I bought my scale, which is made by Hanson, in Shubuta, MS., in a regular hardware store. It's called the Viking, Jr.
After using this scale for a few years, I started to feel a little concerned about it's accuracy. So I brought in a consultant to check the doors for me. After using his fancy test equipment (which didn't look all that different from my little scale - but cost a whole lot more!! /w3tcompact/icons/shocked.gif), it turns out my scale was only off by about 2 lbs. Not bad, really. Now I simply adjust my readings by that 2 lbs., and I'm right on.
So I think for your intended purposes, your scale should be O.K. Like Bird said, if you can, have it calibrated against another scale just to ease your own mind. /w3tcompact/icons/smile.gif