Section 4(1)(C) in The Indian Police Service (Pay) Rules, 2007
(C)Where a member of the Service continues to draw his pay in the existing scale and opts for revised scale from a date later than the 1st day of January, 1996, his pay from the later date in the revised scale shall be fixed under these rules and for this purpose his pay in the existing scale shall be the same as of existing emoluments as calculated in accordance with clause (A) or clause (B), as the case may be, subject to the conditions that the basic pay to be taken into account for calculation of those emoluments shall be the basic pay on the later date and where the member of the Service is in receipt of special allowance, his pay shall be fixed after deducting from those emoluments an amount equal to the special allowance at the revised rates appropriate to the emoluments so calculated.