The gruesome thing about such rating systems, from manufacturers and online shops alike, is, that there is no tranparency about how these ratings are calculated. You have nothing as a benchmark, know nothing about the factors in the background that determine this single figure, and you can even hardly compare one number with the other because everything is boiled down just into one murky number. That's lousy marketing crap, even though the attempt is sensible. But it leads nowhere.
You might take some basic technical figures about a ball and its core (RG, differential, OOB surface prep), but even then I cannot fathom how anyone could compare different coverstock and coverstock technologies, and rate them - and even then it would only make sense for a basic benchmark style or player.
Anyway, a somehow good attempt is IMHO Brunswick's rating, that gives you at least a relative idea of how grabby a ball is, how the breakpoint shape is to be expected at OOB finish and how much (relative) length one can expect. But there's nothing more to deduct from it, and a comparison beyond these numbers can only be made based on subjective impressions.
Maybe, if there'd be a business-wide official standard...? But no manufacturer would hook on this, since it would create lots of pressure to have the "most hooking ball of all time" in the current arsenal, creating too much transparency for the customers.
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DizzyFugu - Reporting from Germany
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