SA

[EmmaG123]

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[#2]

Make sure your numbers are indeed recognised as numbers. I suspect they are not at the moment.

[#3]

I have tried this but having no luck - I should add the ID's are labelled A1,A2, A3 etc. I have tried changing them to raw numbers but the pivot table collates the data wrong

[#4]

In that case all you can do is use a different field to sort on, or change the ID field so it contains A0001, A0002, ...