People sometimes measure "average pace" in different ways. For short rides it is easy, just do the math. Riders who do long distances will often subtract their time at stops from the calculation. For example, doing a 6 hour century using "total elapsed time" would give you a 16.7 mph average, while if 6 hours was your moving time (still 16.7 mph) then your overall start to finish time might be 7 hours which would otherwise calculate to 14.3 mph. Some computers will calculate moving time for the average pace while others will adjust the data manually. With these options it might be hard to compare results.

FWIW: I always considered a sub-6 hour century a good result (total elapsed time) for the typical century which has 3 or 4000 feet of climbing. That is not a reachable number for me anymore.