Lloyd778:
78.1C vapor temp is 95.5% alcohol while 98C vapor is 19% alcohol.
That numbers are no constants for every location on the world. The boiling point of liquids or liquid mixtures is heavily dependent on the air pressure. And the air pressure is heavily dependent on the height above sea level. So if you live at the sea shore the boiling temperatures are different than when living on a mountain.
I.e. pure water at sea level boils at 100°C, but at 1400 m height above sea level the boiling point of pure water is 95°C.
Calculations with Arduino 'float' numbers are not a big problem, even in complex calculations, as long as you don't need to calculate more than 6 significant digits.