I apologize, as this has likely been asked a million times....

I would like to know the formula to calculate water removal requirements to bring sap or concentrate from "Brix in" to "Brix out".
I don't want another chart, or a rule of thumb or a ball park.... I'd like to know the real formula ... that someone is using to make these charts.
I'm a bit of a MS.Excel nut... trying to make myself a calculator... And all these approximations are driving me "nuts", as they don't quite match up with each other....
Can anyone direct me to the real deal, formula or data??

Thanks