The numerical abbreviation sets which abbreviation to use for scale prefixes of numerals, for example M for mega or a million (106), and µ for micro (10-6).
You set the NumericalAbbreviation variable to a string containing a list of abbreviation definition pairs, delimited by semi colon. Each abbreviation definition pair should contain the scale (the exponent in decimal base) and the abbreviation separated by a colon, for example, 6:M for a million.
The default setting is '3:k;6:M;9:G;12:T;15:P;18:E;21:Z;24:Y;-3:m;-6:µ;-9:n;-12:p;-15:f;-18:a;-21:z;-24:y'.
This setting will change the prefix for a thousand to t and the prefix for a billion to B. This would be useful for financial applications where you would expect abbreviations like t$, M$, and B$.