Parametricising a cubic curve

fr gh3d

Hello everyone,

                        can someone tell me how I can parametrise this curve that I have been able to create. I need to do so, so that I can allow the curve to take different ration of the deflection to the horizontal distance.

Using the range points I am able to make the curve take various deflection heights but don't think that is the right way of making it do so.

Please help.

Nikita