Dear Maria,
as Marko already pointed out, use "register to mean".
SPM realigns the data the way the volumes are entered, independent of their names. So if you load *63* as your first volume and go on with 1, 2, ..., then SPM realigns them accordingly. The values within the rp file correspond to the displacement relative to the prior volume (prior defined by the order in which the data is loaded into SPM). But when adding the realignment parameters as regressors during single-subject analysis the parameters should be in a chronological order of course.
Best,
Helmut
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