20.—(1) Where a claimant's income consists of earnings from employment as a self-employed earner his average weekly earnings shall be estimated by reference to his earnings from that employment over such period as is appropriate in order that his average weekly earnings may be estimated accurately but the length of the period shall not in any case exceed a year.
(2) For the purposes of this regulation the claimant's earnings shall be calculated in accordance with Section 4 of this Part.