6. On any pay-day—N.I.
(a)“the normal deduction” is arrived at by applying the normal deduction rate (as specified in the relevant attachment of earnings order) with respect to the period since the last pay-day or, if it is the first pay-day of the debtor's employment with the employer, since the employment began; and
(b)“the protected earnings” are arrived at by applying the protected earnings rate (as so specified) with respect to the said period.