The body was used as the earliest tool for measurement. Of the tools found by archaeologists, the oldest tool used for measurement was the compass. It was used to ensure two stones, when cut would fit together accurately. This aided in the pyramids construction.
ruler Many early units of measurement were based on human proportions, such as a stride (roughly a yard) or the length or an arm. A hand (4 inches) is still used to measure the height of horses and ponies. The first join of the thumb is roughly 1 inch.
Feet, hands, arms...some early measurements were actually based on the average size of certain body parts, such as the biblical "cubit" which was supposed to be the length of the lower part of the arm. Another example is how horses are still measured to this day, by "hands."