This is a set of cards, sorting lid, and keys to teach binary numbers from 0 to 31 OR to use to teach the concept of sorting via dichotomous key with T/F, Y/N questions. The long square keys are for True or 1 bits, the long cylindrical keys are for False or 0 bits. Print 5 each of the T and F keys, one sorting lid, and 32 blank cards, then use diagonal cutters to cut either the square "True" or "1" or "Yes" notches, or the "False" or "0" or "No" notches, out of the upper edge of the cards. An example "10100" or "decimal 20" card is included as an example. (you could design and print 32 different kinds of cards, but really, it's easier to just print them all blank and cut them.) Obviously this is a very simple example of something with a very long history: Jacquard looms, Hollerith cards, the McBee keysort system, etc. This is a simple intro to the concept. With a change in scaling this could also accomodate standard index cards, punched with a one-hole punch. EDIT: finally got to print a trial of this, uploaded resized T and F keys that should fit better in the card slots to allow freer movement. OH NO- problem with the printer, interfering with optimizing this design and getting example prints made. This will be addressed as soon as I'm printing again. Basic use: Stack the cards (aligned with their bevel on the right side) in the sorting lid, which is also beveled. Slide the proper keys into each of their holes. They are indexed so that they only go one way, and each has a flat end for writing 1 or 0 or T or F or other code on the end. When you pick up the lid, only the properly-coded card should fall out. For instance, if you have properly cut out your notches in the cards, inserting 1,1,0,0, and 0 keys in that order (left to right) should allow only the decimal #24 card to fall out. For teaching dichotomous or single-key sorting, assign each set of holes a Y/N or T/F or other question. By answering each question, only the cards satisfying all the conditions will fall out when the lid is picked up. Possible questions to ask: Why doesn't this work (i.e., multiple cards fall out) if you only put keys in the "1" positions? Isn't a 0 just like having "nothing" there? When making a dichotomous key, you are selecting only for the card(s) that satisfy "A" condition AND "B" condition AND "C" condition, etc. This is the AND function. How would you make a system that uses the OR function? What would be the best questions to ask to sort out single students in our class, with the least number of Y/N questions? Demonstration: by using only one T key, you can do the classic "binary sorting" trick to sort shuffled number cards back into numerical order.