At 710, after our rookie year finding out we were 15 pounds overweight, with our wonderful bathroom scale and pieces of wood, it said we were right at 130. Thinking we were safe we got to competition and found out we were 15 pounds overweight. "Say what" yes 15 they said. We proceeded to rip off the mobile goal hooks, then the drilling started with the 1 inch dremming bits, and the massive aviation snips. It wasn't till 500 holes later that we made weight. We realized at that point it was imperative to have a very accurate scale. So in 2002, I said no more guessing, and I took the project on myself to find an accurate scale that we could get accurate weights that the bot could actually sit on without large 4x4's supporting it, because if your not centered, your weight could be off by 5 or more pounds easily. The bathroom scale with the little platform or the feet shaped platform just wasn't cutting it for us. I search long and hard to find something accurate and finally, there was something within our budget accurate enough, and the hardest thing was, the big platform. I then found the best possible price for it. I learned a lot about scales during my search, counters, legal, gram, how they work. I finally found a group of scales that fits exactly the amount of accuracy we needed and the budget for it. Ohaus had the best scales for this application. The series I chose was the ES series and the model was:
Ohaus ES100L its specs, are 220lbs capacity with a tolerance of 0.1 but the selling point of this scale was the fact that it has such a large base for a bench scale. The lowest price I found for it was 289$.
The one I debated only other model I looked at that was somewhere near the price range with a large base was the
Ohaus multi-function CQ100L31 , its specs are a 250 pound capacity with a tollerance of .01 I liked this one better because I could use it to accurately weigh small items to get a general weight during the design phase of the robot. But since we already had a accurate 2000 gram scale it didn't make any sense to buy a super accurate scale, and also the base is smaller than the ES model. The selling price for this scale the lowest I could find is 678$.
One of the things I learned about scales was their tolerance changes by weight, its the most accurate in the middle of its spectrum. For instance a 30 pound max scale is a bad choice for FIRST because it would be too close to its max. You want to chose one with at least a 30 pound difference between its max weight and your robots max weight to get an accurate reading.
Both scales I cited came from the same company
www.discountscales.com I have bought from them before and they are a trustworthy company.