SSRS scatterchart X sort

Hi,

I created a scatterchart. All is well but the X axis labels come out unsorted.

Ex: the x axis should start with -20 and continue with interval of 20 untill it reaches 80.

I've set the above in the chart properties X axis tab (minimum, maximum and interval).

But the X axis is displayed in unsorted order, ex:

4, 1, 9, 5, 2, 5, 3

how do I define it to display  in asc order?

Namnami