It is still not clear on how to find the linear range of the BET plot for microporous materials in a way that reduces any subjectivity in the assessment of the monolayer capacity. A crowd-sourced study involving 61 research groups has shown that reproducibility of BET area determination from identical isotherms is, in some cases, problematic. Rouquerol et al. suggested a procedure that is based on two criteria:
* C must be positive implying that any negative intercept on the BET plot indicates that one is outside the valid range of the BET equation.
* Application of the BET equation must be limited to the range where the term V(1-P/P) continuously increases with P/P.
These corrections are an attempt to salvage the BET theory, which is restricted to type II isotherms. Even while using this type, use of the data itself is restricted to 0.05 to 0.35 of , routinely discarding 70% of the data. This restriction must be modified depending upon conditions.