Lets dig into some juicy details!

This calculator can only add,subtract, multiply and divide single digits. This also includes the answer digit-It can only solve a number up to 9. Please use your damn fingers and toes for sums exceeding the machines capability.

Using all vacuum tubes for switching this relies on the power of the pentode to form flip flops using a single tube. Its lightning quick processor speed is about 1 khtz(SO Fast) and gives answers speedy quick. The large display eliminates the need for glasses and are made from neon bulbs. The power supply sports an unholy 5R4 rectifier pumping out enough heat to prepare a 3 course dinner for two. An OA3 regulator keeps the high voltage B+ in check and stable during operations.

The card reader uses 3 D printed cards specially formulated with magnetic dots to rapidy enter numbers and functions(+,-,* and divide) quickly and outputs to a massive bank of relays that interface with the machine. I also added a massive keypad using the largest and bulkiest pushbuttons I could find for input.Another massive bank of relays interfaces this keypad to the CPU.

If you are forgetful of your sums I also wired in a thermal printer to print out the results of your calculating labors. It does require a wall wart power supply but don't worry it is much more energy efficient than the rest and you will barely notice the extra load on your electric bill using it.

You just have to really appreciate the speed that this thing can carry out stupid simple math! What a wonderful age we live in.

And lest you forget, the tube circuitry is immune to typical silicon frying EMP. You can sit in a dirtpile that used to be your home after the apocalypse and do simple math as long as your generator keeps running.

can you post some documentation on the card reader?