how to calibrate df1 front tank

[fidds]

Have recently purchased a kv 8 row maize drill with a accord df1 front tank for fert how do I calibrate it

 

[Case290]

Guess your measure the land wheel circumstance ie 1.5m then width of the drill ie 4m
One ha is 10000sq/m
One turn =6sq/m / 10000 1666 turns =1 ha
1666/40 = 41 turns of the land wheel weigh x40 = kg/ha alter to