Actually, he has to provide the offset on one

Actually, no. Cross correlation can be used to determine the required offset.

From the Wikipedia page (my emphasis):

Explanation

For example, consider two real valued functions f and g that differ only by an unknown shift along the x-axis. One can use the cross-correlation to find how much g must be shifted along the x-axis to make it identical to f.

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In reply to Re^6: Calculating cross-correlation by BrowserUk
in thread Calculating cross-correlation by Anonymous Monk

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