calculator vs reckoner

calculator and reckoner both are nouns.

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

As nouns, calculator and reckoner are synonyms defined as:

calculator and reckoner: an expert at calculation (or at operating calculating machines)

Other synonyms of calculator include computer, estimator, figurer.

calculator (noun)	reckoner (noun)
a small machine that is used for mathematical calculations; can be mechanical or electronic	a handbook of tables used to facilitate computation
an expert at calculation (or at operating calculating machines)	an expert at calculation (or at operating calculating machines)