plotting the diffrence of a user define function from two data sets

[Ilukpitiya Mudi S P Jayawardena]

Hi

I need to plot the difference of a defined variable from two data sets. when I open the two ctl files of respective data sets and defined the function from 2nd data set as 'define x2=var1.2 + var2.2' a error shows. It mentioned as  'data request warning : request beyond file limits ' . but when I defined the function for 1st data, such as 'define x1=var1.1 + var2.1', it works.


Please help me

Thanks

Ilukpitiya