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Can anyone please tell me what I'm doing woring?
You're not obeying resolution (DPI). Maker sure it's consistent across documents.
To avoid confusion, make sure that both of your documents are with the same zoom level. The zoom level is always displayed on the title bar of your document after the file name and also at the bottom left of the document window where you can type the same zoom for both documents. Then there will be no surprises when you copy paste between the two.