A landlord may charge for an apartment unit a "base rent" equal to that validly charged on May 31, 1978, or on any later date when the tenancy by a tenant begins of an apartment unit which has been voluntarily vacated. Such base rent may be recomputed annually after a full year has elapsed from May 31, 1978, the date of the commencement of the tenancy, or the date of the last recomputation, whichever is later, so as to increase it in accordance with the provisions of this chapter. (1962 Code § 11-3.02; amd. 1988 Code)