Filter paper activity (FPU) was devised by Prof. T.K Ghose for measuring overall cellulase activities. However, the most critical point of this assay was the release of exactly 2mg glucose from the Filter paper. Since the traditional Trichoderma cellulase system was deficient in beta-glucosidase activity, the product released lost its linearity beyond 2 mg and reached saturation. Now the present formulations, not only rich in beta-glucosidase activity due to genetic manipulations and overexpression but have high LPMO activities too which stimulate hydrolysis through unconventional ways. In such a situation, how relevant is it performing the FPU assay correctly and observing exactly release of 2 mg glucose and further dosing the cellulase cocktails on FPU basis?