Chop saw angle setting thingy.

Hi All,
I may have imagined this but I seem to remember seeing someone (could have been on TV) using bit of plastic cut at useful angles, 45, 12, 90 etc for setting the blade on a chop saw. I've tried home made ones but they're always just off true or get damaged and the markings on the saws are +/- 10 degrees or at least thats what it feel like.
Has anyone seen one online, or did I imagine it?
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