Y axe always visible

I'm drawing a graph like behind using core-plot. I wanted to put de Y axe out of the "plotAreaFrame", like that I'll be able to see it all the time, even when I'm scrolling on the X axe.

If it's not possible could you give me a clue to make the Y Axe always visible.

Edit: May I do this by draw开发者_如何学Cing an other chart an displaying only the axes of the second graph and no datas on it?

y.isFloatingAxis = YES;

That was just that line!

In the newest version of Core Plot, isFloatingAxis no longer works, but this does:

y.axisConstraints = [CPTConstraints constraintWithLowerOffset:0];