15.78.3  ERROR 

This specifies the error on the value you  have  specified.   If  you  use
NOERROR  the  error  analysis is turned off.  This only works when you are
modifying X,Y,Z values.   The  specified  error  is  used  to  modify  the
DX,DY,DZ value.
                                  example
     Y=Y * 5.0
Will multiply each Y and DY value by 5.0.
     Y=Y * 5.0 ERROR=0.1
Will multiply each Y and DY value by 5.0.  The specified error of 0.1 Will
be used to compute the actual DY value.
     Y=Y * 5.0 NOERROR
Will multiply each Y value by 5.0.  The DY values will remain unchanged.
     Y="LOG(YV)" NOERROR
Will  take  the LOG to base 10 of each Y value.  The DY values will remain
unchanged.
     Y="LOG(YV)"
Will  take  the  LOG  to  base  10 of each Y value.  The DY values will be
modified as:  DY=ABS(LOG(Y+DY)-LOG(Y)).