While we are discussing NON-linear & linfitCheby
1. NON-linear as applied to a short range of °C saturation
2. linfitCheby as something else ... seat down solid,
otherwise you may drop dead at the attached horrible maths.
Observe how involved the region 1 is on the full range °C.
In other words: fitting a short region is a much different
matter than fitting the entire physics.
Good thing is was done much previous 1997 and before computers,
no fitting tools for that one, not needed either !

Jean

Inst_IAPWS region 1 QUICK.sm (15 KiB) downloaded 68 time(s).