I know, right? Not just by default it's not even an option! They have dozens of paid laser etched add-on option designs but none of them are a ruler, and if you upload your own custom design there is no guarantee it would be to scale. It was the only real thing that made me hesitate. I still like it without the ruler, but I would be near perfect with one.
Honestly I didn't use the ruler all that much (a few times per year) but it was really handy when I had it.