6.3.4 Finite Difference (TYPE2)

UVDIF (N,X,Y1,Y2) Fills the space between 2 lines with a tone pattern.
UHDIF (N,X1,X2,Y) Fills the space between 2 lines with a tone pattern.
UVDIFZ(N,X,Y1,Y2,ITP1,ITP2) Fills the space between 2 lines with a specified tone pattern.
UHDIFZ(N,X1,X2,Y,ITP1,ITP2) Fills the space between 2 lines with a specified tone pattern.