



 
Hi Dan. I agree with all your calculations. When the barrel is empty, there are zero gallons and the "height" of the water is 0 inches. When the barrel is full, there are 62.6 gallons in it and the height is 35 inches. So you have a simple ratio. Every 35/62.6 = 0.56 inches corresponds to 1 gallon. Every inch corresponds to 62.6/35 = 1.8 gallons. So you can read off the inch depth markings and multiply by 1.8 to get your gallons. Or you can mark off the 10 gallon line at 5.6 inches, the 20 gallon line at 11.2 inches, and so on. Hope this helps,  


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