18 October 2011
The concept is to applied when we receive some arrear salary in the current year:-
Relief is to be given u/s 89(1) when we are paying more tax on arrears received in current year if calculated under current years income than if it was calculated in that year in which the income was actually received.
So to the extent of extra tax payable a relief is given u/s 89(1)
Check this link http://www.simpletaxindia.org/2011/04/891-relief-calculator-for-arrears.html