Originally Posted by kv501

I work for a large agricultural manufacturer, and grain carts are part of our product line. As an option, you can purchase a scale kit, which is basically a special axle spindle with a strain gauge built into it. In a nut shell it tells a farmer how much weight is in the grain cart, and from that extrapolates the total bushels of grain.

Your question about the innards being expensive...the scale kits we use operate on the same general principle as a bike power meter; just on a smaller scale. Our cost alone per unit is several thousand dollars, but the most important thing to take away is that you wouldn't believe the amount of development and engineering that goes into these things. The materials and processes aren't what's expensive, it's the research, testing, software development, and trying to make something extremely delicate but at the same time rugged.

You aren't going to rapid fire thousands of power meters a day off of machines in a sweat shop and have them be accurate and reliable. That's why you don't see a $200 power meter out there.