My mechanical calculator is based on this triangle, but by using simple mechanics the triangle formed by the frog's feet and his clasped hands can move. A single card will show the whole multiplication table, and watching it move around is a whole lot more fun than flashcards.
I should say that I did NOT come up with the concept: William Robertson, in 1916, designed a tin toy he named the "Educated Monkey." When I fist saw it a few months ago I thought it would be fun and easy to reproduce the idea on paper -- I was dead wrong.
My desk has been strewn with pins and frog body parts for weeks as I've been trying to fine-tune the template. Changing the monkey into a frog was easy and natural; the way the creature moves is much more frog-like than monkeyish. Getting everything to line up properly was a bit tricky, but manageable. I was able to improve Mr. Robertson's design by figuring out a way to display when a number is multiplied or added to itself (i.e. 5+5) He just drew a little square which represents the number, but my template shows the actual number (you can't see me right now, but I just patted myself on the back). I found tiny aluminum eyelets at a paper supply store, but during the design process, for expediency, I used pins sticking up and tried not to injure myself as I banged my desk in frustration... Because after getting everything to work perfectly, when I finally printed my frog out in color, cut the pieces for what I thought would be the last time and used the cute little eyelets --- it didn't work. The pins I had been using held the paper body parts in place while allowing them to pivot freely. The eyelets, on the other hand, held the paper together too tightly, so in a few critical places instead of pivoting the paper stuck and buckled instead. The d... thing needs to be made with a stiffer material after all.
Step 1: Materials and tools
the PDF template
A scalpel knife (also known as an Xacto knife) with a cutting mat to protect your table
An empty tea box
A hammer (with a nail or screw)
A dremel tool or any other rotary tool which will cut through thin sheet metal
Small aluminum eyelets and a matching setting tool (I got mine from the Paper Source)