If you tell me how wide your seeding tool is, I think I can look up how many turns = 1 Acre.

When you know that, you can open the bottom flap and turn the specified number of turns, weigh the product that falls in the bucket, and go from there. That's a rough estimate. For real fine calibration, you need to secure the big hose in a gunny sack, turn on the fan, turn the crank at approximately the speed it will turn when seeding (for the required number of turns), and weigh what collects in the sack.