The PDF you link to is indeed outdated. Please follow the latest tutorial instead
As far as I can tell, however, your issue does not come from PCIbex, or from the way you calculate RTs per se. It comes from the fact that some values (fr51, fr24, …) were entered on several occasions, for multiple submissions. As I mentioned in my previous message, and as suggested by the IBEX manual, you could group by MD5+ReceptionTime instead of, or in addition to, ID (which turned out to not uniquely identify submissions, as we found out): group_by(group, Results.reception.time, MD5.hash.of.participant.s.IP.address, ID, entry). But at the end of the day, if you initially assumed that ID should uniquely identify submissions, you should probably try to figure out why that turns out not to be the case
Jeremy