Concept:The abacus is recognised as the earliest known device built for counting and simple calculations.Explanation:The abacus is an ancient manual tool that was used to perform arithmetic operations.It consists of beads or stones arranged on rods or in grooves to represent numbers.This device dates back to around 3000 BC, long before other calculating machines were invented.Hence, among the given choices, the abacus is the first calculating device.Answer:A. Abacus