text: Terrell L. Hill described BET as a theory that is "... extremely useful as a qualitative guide; but it is not quantitatively correct". Although BET adsorption isotherm is still extensively used for different applications and is used for specific surface area determinations of powders whose calculation is not sensitive to the simplifications of the BET theory. Both Hackermans and Sings group have highlighted the limitations of the BET method. Hackerman et al. noted the potential for 10% uncertainty in the methods values, with Sings group attributed the significant variation in reported values of molecular area to the BET method's possible inaccurate assessment of monolayer capacity. In subsequent studies using the BET interpretation of nitrogen and water vapor adsorption isotherms, the reported area occupied by an adsorbed water molecule on fully hydroxylated silica ranged from 0.25 to 0.44 nm².  Other issues with the BET include the fact that in certain cases, BET leads to anomalies such as reaching an infinite amount adsorbed at  reaching unity,  and in some cases, the constant C (surface binding energy) can be determined to be negative.