BTW - I'd be perfectly happy to work this out on my own if anyone could give me the formulae - or tips on where to find the info.

Thanks

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Talent develops in quiet places, character in the full current of human life.
- Goethe

Jump in with both feet!
- Me, indulging my inner eight-year-old

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"Are you a mad-hatter that just types what he wishes, or have you actually any physics training?"
Occam's Ghost to Grant Hutchison.