Calculus is nothing more than counting by making piles of stones.I thought it came from dentistry.
The best stones were kidney stones. The stones were calcium, which means the same thing and is also from the root as the word for counting stones. The first mathematicians were Egyptian (Africans, since Egypt was Africa at the time), who used various surveying calculations not only for relocating their planting fields after the frequent flooding, but also for laying out the massive stone constructs which they also needed as initial points to relocate their planting fields. The abacus was Greek, the Greeks having little use for it since they did not trade extensively, although it became popular in Asia due to its application in trade once Rome became wealthy enough to engage in commerce.