If cargo insured against partial loss arrives at the port of destination in a damaged condition, the loss of the insured is computed as follows:
(a) Deduct the market price, at port of destination, of the damaged subject matter from its market price there when sound.
(b) Take that proportion of the value which the remainder thus ascertained bears to such market price when sound.
(Enacted by Stats. 1935, Ch. 145.)