Section 5(1)(b) in The Indian Police Service (Pay) Rules, 2007
(b)if he was holding a Class I post before appointment to the Service, his pay shall be fixed at the same stage as the pay in the Class I post if there be such a stage in the Junior Scale admissible to a member of the Service, or at the next lower stage, if there is no such stage in the Junior Scale admissible to a member of the Service and where the pay so fixed in the Service is less than his pay in the Class I post, he shall be allowed the difference as personal pay to be absorbed in future increments; and