It is a very relative thing, and since many factors influence the ball reaction beyond oil volume (PAP, speed, revs, lane surface, even air humidity), this can only be a relative indication of what a manufacturer's balls are able, at OOB, under controlled (and unspecified) conditions, ideally. Lanemasters has a similar chart, an if I remember correctly Roto Grip, too.
While I would not take the chart for "true", and in some cases the ball figures had been way off reality (e. g. Smokin' Inferno), I consider it a good help when you want to build a single manufacturer arsenal, or have an indication what the OOB ball is designed for.
Comparing different manufacturers' products is another thing, and VERY tricky (See above) - and putting this into a (simple) rating system that is supposed to be "objective" is IMHO impossible, wishful thinking or total ignorance.
That's why BR.com's and other sites' reviews is so valuable: lots of subjective impressions that allow an assessment of a ball's (relative) potential. Manufacturer's input can help, but is IMO only half of what you should know about a ball.
--------------------
DizzyFugu - Reporting from Germany
Confused by bowling?
Check out BR.com's vault of wisdom: the unofficial FAQ section
