These are two different types of enzyme activity assays. While Sinha (1972) describes a discontinuous enzymatic assay, Aebi (1984) reports a continuous assay. Discontinuous assays need the reaction to be halted and a following procedure to determine the levels of remaining substrate or product. On the other hand, the concentration of substrate or product is monitored without interruption in continuous assays.

Note that in Sinha (1972) "The catalase preparation is allowed to split H2O2 for different periods of time.". Thus, it is not a single reading. There are several end-point readings at different time points.

I would recommend the use of a continuous assay, such as that described by Aebi (1984).

See also:

Welker, A.F., Moreira, D.C., Hermes-Lima, M., 2016. Roles of catalase and glutathione peroxidase in the tolerance of a pulmonate gastropod to anoxia and reoxygenation. J. Comp. Physiol. B 186, 553–568. doi:10.1007/s00360-016-0982-4

Sinha, A.K., 1972. Colorimetric assay of catalase. Anal. Biochem. 47, 389–394. doi:10.1016/0003-2697(72)90132-7

Aebi, H., 1984. Catalase in vitro. Methods Enzymol. 105, 121–126.

Dear Daniel...

I genuinely dont know about discontinouse and continouse methods but if you are trying to say that Sinha protocol is discon. becoz it has different time intervals then i just acknowlwdge you, in case of Sinha protocol there are two wavelength consider. in discontinouse assay reading take at 610nm with different time intervals but in continouse assay reading take 570nm(single reading).According to protocol.

My query is about the calculation methods becoz in case of Aebi(240nm) or Sinha(610/570nm) there are huge distance b/w absorbance spectra and definitely results VARY.Then how can I say taht my Aebi calculation is correct or either Sinha ?

In overall without any spectrophotometric error results are not correct.

and thank you for your valueable suggestion.