Once a use, building, structure, lot, parking space, loading space, sign, landscaping or any other activity which had been nonconforming is brought into conformity with this chapter, it shall not be permitted to revert to nonconformity. Once a use, building, structure, lot, parking space, loading bay, sign, landscaping or any other activity which is nonconforming is brought into closer conformity with this chapter (i.e., the amount or degree of nonconformity is reduced), it shall not be permitted to revert to nonconformity with the provisions of this chapter which is greater than the closest amount or degree of conformity which it has achieved.