This week's Illustration Friday topic is subtract. It got me thinking back to learning basic math facts in elementary school. Being a child of the 70s my parents bought me the "Little Professor" calculator to help me practice my math. An electronic version of flash cards.
I actually found this in the basement a year or so ago (the benefits/curse of being in a family of pack rats) and it still worked. I gave it to my oldest daughter to use but I believe she just thinks it's an antique. (and she's not necessarily wrong)