How exactly is the value of terraforming calculated as a function of the concentration of oxygen in the atmosphere, the average (!) air temperature and the average pressure at sea level? In other words, if I want to develop the "terraforming" discovery branch faster and it doesn't matter to me whether to give preference to "oxygen", "heat" or "pressure", what exactly influences the progress of "terraforming" to a greater extent? How many "Ti" are there for each percent, kelvin and pascal respectively?

From the Fandom wiki

The index is calculated as follows:
Ti = Oxygen (in ppq) + Heat (in pK) + Pressure (in nPa) + Biomass (in g).