Character Set A: encodes all upper case ('A=33' to 'Z=58') and ASCII control characters ('NUL=64' to 'US=95');
Character Set B: encodes all upper ('A=33' to 'Z=58') and lower ('a=65' to 'z=90') case characters;
Character Set C: encodes numeric digit pairs 00 through 99 ('00=00' to '99=99').
Character Set A and B: used to encode alpha-numeric information
Character Set C : offers double density when being used to encode numeric data, which means use a single value/code, decoded as two digital value/data, that is one value = two data.
This third character set - Character Set C, effectively doubles the code density when printing numeric data.