Thank you very much for all that Paul.
I tried it tonight and made substantial progress but was cut short due to pretty extensive cloud cover...
How long do you let the drift explorer run between adjustments before retargeting? I was doing 1 - 2 mins each hit as I found I got inconsistent readings (ie drift per minute would move up and down) if I did less (I'm guessing due to clouds passing over head and below average seeing - it was very humid out).
Is this too long / too short?
Hope my question makes sense!