Isoline curve lux values is not similar or close to the mesh values

hallo Forum,

I am trying since days but i am still not able to do it. Attached is the gh file. As you can see (after running), the values in the mesh ( lux values) doesn't fit the isoline curves results; and in the isolines curves, when it reach the maximum value , it keeps posting the same value; and the lower values in the curve are not close to the ones in the mesh points.

( i am not able to fix it through average formula or interpolation...i am not sure actually how..)

What i want in the isoline curve is to show values for instance from 100 to 1000 Lux with a step of 100 Lux ( i.e : 100, 200, 300, ..., 1000 ). On the other word, I want the scale to have from 100 to 1000 Lux with a step of 100 Lux.

any idea?

Thanks for your support!

nass.