Is a Defense rating of (for example) C/B the same as B/C ? A/D and D/A ? If not, why not ? Btw, new here and glad to have found you while this weirdness is going on. 30-year Scoresheet vet and their old-timer game was my fave, but happy to try something else.

So the first letter refers to fielding as in not-making errors. The second refers t range factor.

I suggest strongly that you look at the pinned set of threads that contrarian23 has collected on the best of the Forum, and see what there is on defense.

A rating of C is not always the same thing: a player from 1910 with a C will not be the same as a player from 2019 with a C, and a SS with a C is different from a third baseman or outfielder with a C rating.

Those pinned threads he mentions are very informative. Excellent reference material for all of us.

Personally I would rather look at the normalized FPCT and RRF numbers than the letter grades. They help me compare players from different eras on a level playing field.

I highly recommend reading the aforementioned threads as well. My "Fielding for dummies" explanation is "Fielding grade tells you how many errors he'll commit", while "range grade tells you how many hits he'll take away". As others have mentioned, not every letter grade is created equal. But if while searching for players you click on their name, and you look at "performance history", take a look at their Fielding history and pay attention to errors and +/- plays.
A "-" play means it would have been an out, but due to the players range stat, it became a hit, whereas a "+" play means it would have been a hit, but due to the players range stat it became an out. Two players may both have defense grades of C/A+, where one player commits an average of 30 Errors with 20 + plays (a net -10), where the other player commits an average of 50 errors with only 5 + plays.

The A+ and D- grades I understand can be misleading in that there's no limit to their respective ceiling and floor. But generally aren't most grades normalized by position ? Yes, a Shortstop will make more errors than an OF, but if for example they are league average at their respective position, wouldn't they have a similar grade ? Or am I still missing it ?

This early on I notice D has a big pull on salary and am trying to decide if or how much of that bias is warranted or not. Generally, not a big fan of D, even in Scoresheet, where you can regularly count on someone grabbing O.Smith 100 picks early and never finish in the money, all the while I grin.

Great range is pricey. It has a big effect on pitching effectiveness. All pitchers, but especially deadball pitchers produce tons of ground balls. The defensive runs saved is a big factor. + plays are a big deal.

Your infield defense is much more important. Consider the number of chances they get. Hence the importance...

There are set ranges to the letters given to fielding ability. They're posted in the pinned threads if you care do dig for them.