556. For the purposes of computing an income replacement indemnity of a person contemplated in the first paragraph of section 555, the gross income of the person is that(1) which he receives from the employment he holds at the time of the recurrence, relapse or aggravation, or
(2) which he received from any employment he carried on during the 12 months preceding the beginning of his inability to carry on his ordinary employment, if he does not have any employment at the time of the recurrence, relapse or aggravation.