Chart question
 

I have kind of xy-chart.

Values on x and y varies a lot according to calculations so i would like to
fit them to my chart area.
But i would like to fit them so that x equals y, so the scale is 1:1.

- fit x according its max value (enabling 'max value' in chart)
- scale y so that 1:1 scale is achieved. (Here i can't use the 'max value'
in chart, because 1:1 scale can't be achieved)

What to do.

Thank You in advance.