19. For the computation of periods expressed in years, months or days, see Rules 80.1 to 80.3. For the computation of any period expiring on a non working day or official holiday, see Rule 80.5. For the determination of the starting date of the computation of any period and the date on which any period expires, see Rules 80.4 and 80.7. For the computation of any period in the case of delay in the mailing or the receipt by the applicant, see Rule 80.6. For the (re)computation of any time limit where the priority date has changed, see Rules 26bis.1(c) and 90bis.3(d) and paragraphs 192 and 321.