Material usage operational variance

Sir second question .why we calculate the variance of efficiency by standard unrevised budget rate to get labour efficiency operational variance?

As I explain in my free lectures there are two ways of calculating the operational variances (using either the original budget cost or the revised budget cost), which give different answers. The old examiner preferred one way and the current examiner prefers the other way (although either way always gets full marks). If you watch my free lectures on this, then I explain which to use, doing it the way that the current examiner prefers (which is also the easier way :-) )