On that page are links to all the Rigsby progenitors. The part to the left of the first dot in your R-number tells you which is yours. From there, follow the children whose birth order corresponds to each segment of your R-number until you get to the Rigsby in question. For example, to find R05.5.7.1, start with R05 James, then his fifth child (James II), then James II's seventh child (James W), then James W's first child (James Walter).
If you have information about anyone here who doesn't have an R-number, please contact me.
Note: These links all worked at the time I visited them, but may or may not now. In some cases the target site may have been rearranged, so you might have to re-search that site to find the Rigsby records.
HOW TO READ THESE ENTRIES
Ancestry.com births: date, child name, s/o or d/o, parents, R-number