There is also a mode function that finds the most common value in a matrix; you can turn it into a column function like this:
dt = Open( "$sample_data\big class.jmp" );
dt << New Column( "age centered on mode",
formula( :age - As Constant( Mode( dt:age << getvalues ) ) )
);
The <<getValues message returns a matrix of values from the age column. The AsConstant function calculate the mode once, and treats that value as a constant for the rest of the column (speeds it up, not strictly necessary).
Column using Mode
You can change mode to mean and see a different set of numbers.
Craige