Math Is Fun Forum

Dear fellows:

I have seen a simple chart but find out figure out how it is generated. see images

The horizontal axe is the loading width of a panel (say x ), the value at vertical left is the loading height, with this two parameter (say y) , it comes to a points,  the vertical axe at right is the target value (say Z),

Z is properly euqals xy³ or xy².

Is anyone here familiar with this kind of chart and kindly tell me how to make it with my own.

Thanks,