15.64.49.10  POWER|ROOT  - This sets the scale to be the selected power or
root.  N must be in the range 0.1 to 100.  If n is  not  specified  it  is
assumed  to  be  2.   The  sign of the axes is preserved to avoid multiple
values.  The rules for determining ticks and labels are the  same  as  for
linear scales.

                                  Example
     TD:SET SCALE Y ROOT=3
Y is scaled as Y'=SIGN(ABS(Y)**(1/3),Y)
     TD:SET SCALE X POWER=2
X is scaled as X'=SIGN(ABS(X)**2,X)