The circumference divided by the diameter is always the same number

Try to measure a circle.The diameter and radius are easy,they're just straight lines you can measure with a ruler.But to get the circumference, you'd need measuring tape or a piece of string,unless there was a better way.Now, it's obvious that a circle's circumference would get smaller or larger along with its diameter,but the relationship goes further than that.In fact, the ratio between the two,the circumference divided by the diameter,will always be the same number,no matter how big or small the circle gets.