Green’s Dictionary of Slang

to calculate, to think out.

1836		T. Haliburton Clockmaker I 40: If a man knows how to cypher, he is sure to get rich. We are a ‘calculatin’ people, we all cypher.
1848		J.R. Lowell Biglow Papers (1880) 120: I made my darkies all set down around me in a ring, / An’ sot an’ kin’ o’ ciphered up how much the lot would bring.
1855		T. Haliburton Nature and Human Nature I 43: I leave you to cypher that out.
1862		J.R. Lowell Biglow Papers 2nd series (1880) 75: I’ve made my ch’ice, an’ ciphered out, from all I see an’ heard.
1872		‘Mark Twain’ Innocents at Home 441: He got to comin’ down the shaft [...] to try to cipher it out.
1884		(con. c.1840) ‘Mark Twain’ Huckleberry Finn 168: Leave me alone to cipher out a way so we can run in the daytime if we want to.
1896		Ade Artie (1963) 49: The next thing I can cipher out was that we go to the restaurant.
1907		W.M. Raine Wyoming (1908) 55: I’ll cipher out somehow to be there.
1986		L. Heinemann Paco’s Story (1987) 14: We ciphered it out right then and there that we couldn’t dig a hole deep enough.