Bettison drill calibration trouble

[Peacock5305]

I have a bettison tc3 drill four mtr 175mm row spacings 16 tooth drive on12.4-24 tyres. It never came with a manual and the only one i could find is for a tc4. I am wondering if anyone has an idea how many times you are ment to turn the calibration handle and what you multiple the weight by.

 

[eagleye]

always used to do it ffrom first principles.
4 meter drill for every hectare does 2500 meters in straight line or roughly 1000 meters per acre
or tenth acre equals 100 meters
measure height of 12.4 x 24 wheel in meters and multiply by 3.142 to give circumference (or could put chalk mark on side of tyre and ground get someone to drive drill forward for one reveloution and measure distance travelled)
divide 100 (meters) by circumference of wheel (in meters) = number of times wheel revolves for tenth acre.
you can then turn calibration handle and count numbers of times wheel revolves to see how many turns it should be (likely need drill jacked up so wheel can be turned and coulters down to engage seeding mechanism.
Been using this method for 35 years = fool proof except on newer electric driven drills