Set nominal values for/group a dataset by specifying a fraction which determines how far away from the original value a nominal value can be.
Ex: A set of velocity data:
v = [0 9.03, 0.1, 5.2, 0.101, 0.095, 5.01,0, 9, 4.9, 9.2, 8.9, 5.3];
nomV = setNom( v, 0.1 ); plot( (nomV-v)./v, '*' ); disp(unique(nomV))

Each velocity now has a nominal value which is at max 10% off the real value.