E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
is from the Latin calculi (pebbles), used by the Romans for counters. In the abacus, the round balls were called calculi, and it was by this instrument the Roman boys were taught to count and calculate. The Greeks voted by pebbles dropped into an urna method adopted both in ancient Egypt and Syria; counting these pebbles was calculating the number of voters. (See page 2, col. 1, ABACUS.)
I calculate. A peculiarity of expression common in the western states of North America. In the southern states the phrase is I reckon, in the middle states I expect, and in New England I guess. All were imported from the mother country by early settlers.
Your aunt sets two tables, I calculate; dont she?Susan Warner: Queechy (vol. i. chap. xix.)