2. In the leave year in which a member is appointed to or retires from the force or completes such number of years' service as will entitle him to an increased period of annual leave, his annual leave shall be calculated at the rate of a twelfth of the period of annual leave appropriate, under paragraph 1, to the leave year in question, a fraction of a day being reckoned as a day:
Provided that where a member completes the said number of years' service while completing a month’s service in the leave year in question, he shall be treated for the purposes of this paragraph as if he had completed the said number of years' service at the beginning of that month’s service.