Calculating Seeding Rate - Real World Farm Math 101

Our kids are home schooled, so when I came across a great math problem I decided to include the two older kids in the process. It started by reading the implement manual for the JD grain drill. As I was working my way through the manual I decided I needed to calculate the exact amount of seed being dropped by my brother's drill. My brother had said that he dropped twice the amount of seed that he had intended when he used the drill based on what the manual said, so I wanted to make sure that I didn't run out of seed or waste any seed. Each crop has a recommended planting rate based on pounds per acre, and to get the drill to drop the right amount of seed, adjustments have to be made so that the drill meters out the correct amount. The manual has recommended settings based on tire size and turns/revolutions per acre but they also recommend measuring the amount of seed dropped. To measure the seed we jacked up one side of the drill so that the wheel could be manually turned to drop seed from several seed drops with a fixed number of wheel turns. Then we used our digital scale to measure the amount. The original math we used is
10 turns from 3 drops=0.19500lbs
1 drop 10 turns=0.06500lbs
1 drop 1 turn=0.00650lbs
17 drops 1 turn=0.11050lbs
1 acre is 615 turns=67.95750lbs
This is 67.95 pounds to the acre.
But then I noticed that the tire size in the manual is not the same as the tire size on the drill so our information is WRONG!!!
Next we went back to the drawing board and decided to calculate area covered and seed dropped with tire size being a variable. Since all of our calculations were based on 10 turns/revolutions of the wheel, that was our starting point. 10 revolutions of the wheel moves the drill about 73.5 feet. The drill is 9'4" wide so doing length times width we were able to determine that in 10 revolutions of the wheel we covered .016 acres. Then multiplying by 62.5 to get to a full acre we could calculate the amount of seed dropped in an acre from the weight measurements that we made originally and yes, if we had used the original measurements with the wrong tire size we would have dropped a lot more seed than we should have. Also, doing the math also makes me think that planting with a 9'4" drill is going to take forever!