reckonmaster
/ˈrɛk(ə)nˌmɑːstə/ /ˈrɛk(ə)nˌmastə/rare (historical in later use)
noun
A mathematician; an arithmetician; an accountant.
Origin
Late 16th century; earliest use found in John Dee (1527–1609), mathematician, astrologer, and antiquary. From reckon + master.