reckoner vs ready reckoner

reckoner and ready reckoner both are nouns.

Word	Noun	Adjective	Verb	Adverb
reckoner	Yes	No	No	No
ready reckoner	Yes	No	No	No

As nouns, reckoner and ready reckoner are synonyms defined as:

reckoner and ready reckoner: a handbook of tables used to facilitate computation

reckoner (noun)	ready reckoner (noun)
a handbook of tables used to facilitate computation	a handbook of tables used to facilitate computation
an expert at calculation (or at operating calculating machines)