California Business And Professions Code Section 3366

A licensee shall, upon the consummation of a sale of a hearing aid, keep and maintain records in his office or place of business at all times and each such record shall be kept and maintained for a seven-year period. These records shall include: (a) Results of test techniques as they pertain to fitting of the hearing aid. (b) A copy of the written receipt required by Section 3365 and the written recommendation and receipt required by Section 3365.5 when applicable.