Section 70. Every person to whom a certificate of registration has been granted shall cause the same to be recorded in the office of the clerk of the city or town where he principally carries on the practice of optometry; and if he removes his principal office from one city or town to another in the commonwealth, he shall, before engaging in practice in such other city or town, notify the board in writing of the place where he is to engage in practice, and obtain from the clerk of the city or town where his certificate is recorded a certified copy thereof and file the same with the clerk of such other city or town. The fee for recording such certificate or issuing a certified copy thereof shall be as provided by clause (57) of section thirty-four of chapter two hundred and sixty-two. Every registered optometrist shall display his certificate of registration in a conspicuous place in the principal office wherein he practices optometry, and shall, whenever so required, exhibit it to said board or its authorized representative; and whenever practicing optometry outside of or away from his principal office or place of business, he shall deliver to each customer or person fitted with glasses by him a memorandum of purchase, containing his signature, home post office address and the number of his certificate of registration, together with a specification of the lenses and frames or mountings furnished and the price charged therefor.