Loss due to vacancy, income from house property

I've seen different treatment of loss due to vacancy in computation of income from house property. I want to know which is more reliable or if i am wrong somewhere. Different treatment are as follows 1st Treatment-- a). Calculate Annual let out value,ALV (i.e., higher of MV & FR subject to max. SR) b).then actual rent for whole year after unrealized rent but before loss due to vacancy c). Take higher of a and b above and then deduct loss due to vacancy, result would be GAV. 2nd treatment-- a). Same as above b). If AR after deducting loss due to vacancy and unrealized rent>ALV, then AR is GAV but if i. AR is less than ALV owing to loss due to vacancy. AR is GAV otherwise ii. If AR less than ALV because of any other reason ALV is GAV. . 2nd treatment as per study material from Institute and 1st one in a well known author's book.