Winnie is on the money mate. If you are 20mm out then 10mm of that belongs on each side of dead centre.
If you consider that as George said centre was 100mm then you have a 90mm on the front and a 110mm from the back. This is positive 10mm. 10mm from centre.
Hope that helps





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....... I'm a lucky bugger! I've got 2 of em!
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