It may be noted that marginal variation in Senna occurs due to variation in the moisture contents. It is because of this the BP allows an assay value varying from 5.5% to 8%. It may also be noted that on keeping the solution and taken the reading after longer period of time (15, 30, 45 minutes) the assay value will go up as this is a colour developed method. Hence, we recommend that the reading be taken within one to two minutes after preparation of the test solution.