Last modified: July 11, 2005

This is a modular arithmetic calculator written long ago in JavaScript. It never made it out of its test phase.

Currently, input is only accepted from the buttons.


  1. First define the modulus by entering its value in the topmost window (clicking the "Enter Modulus" button is no longer necessary).
  2. Enter an integer by clicking on numeric buttons.
  3. Most operations (including greatest common divisor, "g") are binary and are entered in "infix" form.
  4. Enter the second operand.
  5. Click on the "=" sign to perform the calculation.
  6. Example: With modulus m = 50, clicking the four buttons 6 * 9 = will yield the answer 4 since 6*9=54 and 54 MOD 50 = 4
  7. The greatest common divisor of integers a and b is obtained as follows:
    1. click in the digits of a,
    2. click on the gcd button.
    3. click in the digits of b,
    4. click on the = sign.
    For example, the greatest common divisor of 192 = 2 6 * 3 and 30 = 2 * 3 * 5 is 2 * 3=6. Note that this is independent of the modulus m: the answer will be the same no matter what value m has.
  8. New! You can now enter values directly from the keyboard into the registers.
NOTE: While the main display field seems to accept keyboard input, the software only reads keyboard input in the modulus field (step 1) and registers (step 8).

Please report bugs to me via e-mail.