The number of extra hours for which a shop assistant has been employed in or about the business of the shop while any one or more orders have been in force under section forty-one of this Act shall be added together, any fraction of an hour not exceeding half being treated as half an hour, and any fraction of an hour exceeding half being treated as an hour.

For the purposes of this Schedule the number of hours comprised in the customary working day on days other than half holidays shall be taken as the standard unit.

The aggregate number of the extra hours, as calculated in accordance with the provisions of paragraph 1 of this Schedule, shall be divided by the standard unit, and the quotient, fractions thereof being disregarded, shall be the number of the days’ holiday to which the shop assistant shall be entitled.