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Thanks OG, for some unknown reason, it was formatted in text how I do not know as it was a new work sheet. Also In Excel 2010 if there is something wrong with the cell, a mark appears in the top left hand corner of the square and on selecting that square a small diamond with a ! in it shows. On clicking on the diamond I have just discovered, thanks to you, that it acually tells you whats wrong and suggests how to correct the error. Up to today when this error sign has appeared, I have just clicked on the Ignore th Error but in this case on looking more closely at the information showing it told me it was formatted in Text and did I want to change it to a number format which I clicked on and Hey Presto it worked so perhaps in future will look at the message more closly. So thanks for all the replies and especially OG obviously a far more cleverer OG than this OG.