11.—(1) In the case of a police officer who has spent one or more periods in part-time service, the number of days of pensionable service in any such period shall be calculated by the application of the following fraction—
Where—
A is the total number of determined hours of part-time service specified under the part-time appointment of the officer in the period in question; and
B is the number of hours per week if the service during that period were on a full-time basis.
(2) For the purposes of paragraph (1) a period of part-time service is to be taken to have ended and another such period to have begun on the occurrence of any change in that fraction.