Help with ChessBase

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NimzoRoy

I've emailed ChessBase a few times with questions that were never acknowledged even with a "form letter" much less answered, so much for their customer "support" for paying customers (I'm using CB9 & Fritz 12).

Anyways I can't figure out what the "null (or "empty") set" symbol (zero with a slash through it) means when used by ChessBase for instance (excerpt from an "Opening Report" follows)

4. Moves and Plans
a) 8...dxc4
61 Games, 1951-2009, Ø=1983
Black scores above average (48%).
Elo-Ø: 2459, 41 Games. Performance = Elo 2388

If anyone out there in cyberland has a clue I'd appreciate being clued in here!