E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Cocker.
According to Cocker. All right, according to Cocker. According to established rules, according to what is correct. Edward Cocker (1631–1677) published an arithmetic which ran through sixty editions. The phrase, “According to Cocker,” was popularised by Murphy in his farce called The Apprentice.
