What measurement tool has been in use since at least 2650 B.C.?
The ruler has a lengthy history. The oldest preserved ruler — a rod made out of copper alloy that dates back to 2650 B.C. — was discovered in Nippur, Mesopotamia (now modern-day Iraq) by a German archaeologist named Eckhard Unger. Preserved rulers have popped up in other locations, such as ivory rulers used in the Indus Valley in 1500 B.C.; it is likely that rulers made of decomposable materials, such as wood, disintegrated over time.
Answer: The correct answer is Ruler.