53.4. For the purposes of sections 50.3, 57 and the sections that refer to section 57, a contributory period is, for each year, the number of contributory days in the period during which the employee was a member of the plan in a year or in the period during which days and parts of a day were otherwise credited to the employee with contributions, within the meaning of section 73, except the days and parts of a day determined by regulation, over the number of contributory days in the year concerned, that is, 200 or 260 days depending on the basis of remuneration for the employment. The contributory period of a new employee for the year during which the employee becomes a member of the plan begins on the first day in respect of which the employee contributed or was exempt from contributions and the last period ends on the last day credited in the year during which the employee ceases to be a member of the plan.