It's Official: We Were WRONG About the Big Bang

I feel like I have a pretty good handle on the expansion of space but the analogy you used brought up a doubt. In the graphic, there was a ruler that was used to measure the distance of the raisins. The ruler didnt expand. Any ruler I can think of would be _in the universe_, so it would expand too. The distance _on such a ruler_ would remain the same.. but we know (or assert) that the ruler stretched so it really is longer than the distance on the ruler.
What ruler do we have that doesn't expand with the rest of the universe?