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Hi David. Can you verify that the pictures you sent are in the right order. Doing shorter strokes centre over centre creates a turned up edge and a hill at the centre which is what you have. The photos seem to be in the wrong order that's all. Not to stress this is easily fixed. Just a couple more 1/3 strokes centre over centre should bring it back. Try 2-3 minutes if there is no movement go for 5. You can also do slightly longer strokes than 1/3, but I wouldn't go this way it may backfire. I know it's tedious but the closer to spherical you get the easier it will be to parabolise. The idea is to reach the parabola without defects. Also I find it easier to parabolise using only one stroke all the way through without having to change to something else in order to repair a defective parabola, it makes for a better mirror.
regards Cristian
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