Black Racing Dials
These are seen in Professional and non Professional versions. Unlike the standard dial, the Professional Black Racing has smaller subdials, and consequently shorter subdial hands. The central Chrono seconds is seen in several executions.
Unusually, the professional version is more sought after by collectors.
Values range from $40,000 to $100,000 and entirely depend on quality.
So far, the consensus between people who might know is that no more than 10 of each are known. However we all know that consensus is not the best foundation for any conclusion.