Here's a fun experiment you can do with your body without the need for any numbers!

On the first day of your next period start drawing notches on some object, say like a saber tooth tiger bone. Every day after that (every time you see the sun), you make a new notch. When you get your next period, you stop drawing notches on the bone and start a new bone.

You'll know when you will have to menstruate when the amount of notches on one bone matches the notches on the other! Yay ^_^

(ps if you haven't figured it out this was how women figured out their menstrual cycles before the invention of numbers)

What else did you learn today?