merging multi-plots into one equation using curve fitting

I have multi-plots as shown, I got a polynomial equation for each curve by using the curve fitting technique, my question is how can I merge all these plots into one polynomial equation, could anyone help ? thanks in advance Note: just the blue curves

[KSSV]

You mean for all the curves, you need a single polynomial equation?

[Oday Shahadh]

yes Sir

[KSSV]

How it is possible?

[Oday Shahadh]

As seen the value of the altitude shifting down the plots

[Oday Shahadh]

I think my be by estimating the shifting value between the curves,