Net national product (NNP) is equal to gross national product minus capital consumption allowance:
NNP = GNP-CCA.
Net domestic product is likewise
NDP = GDP - CCA
(As above, the difference between NNP and NDP is net factor income and unilateral transfers to foreigners.)
The production which has been devoted to maintaining our stock of means of production, that is the capital consumption allowance, must be deducted to see what new consumption and income occurred during the year.