Thanks for your comments but it still did'nt budge I still have one primary y-axis and no secondary y-axis!
This I would like your suggestion on it.
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I have not followed this thread in detail, but this link could be of some help in case you need primary and secondary y-axes:
http://riotorto.users.sourceforge.net/gnuplot/func2d/index.html#secondary
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Mario