What's it called - black and white thingy for museum photography?

I'm looking for some words I can use to get that black-and-white measuring thing that is used by museums in photographs to show how big something is.  

It usually has black and white squares in CM and Inches.  Sometimes it's L-shaped and sometimes it has a middle grey area for better colour editing.  

I can find the fancy forensic version but not the simple one we see in museum photos.  

Any idea what words I can plug into amazon to help me find this thing?  

Are you looking for Photomacrographic Scales?

Photo Scale