Basic Trigonometry is very usefull.
With a bit of practise you will get visual AOB down to +-5Ds (it's not that difficult)
You 'want' to attack at 90Ds so adjust course to AOB+Scope bearing = 90.
Once on course centre scope on target, note your speed and scope bearing.
Adjust your speed so that your target stays on the scope bearing.
From here target speed is just a ratio of your speed and scope bearing.... dam simple
