## On the Subject of Alphabet Tiles

The module consists of 5×5 tiles with different letters, a play button, and a small display with a letter.

To disarm the module, you will need to:

• take note of the grid of letters and the letter from the small display;
• press the “Play” button;
• take note of a sequence of 6 letters that cycles;
• (during the cycle, the microphone button can mute/unmute the sound);
• perform a calculation that results in a letter;
• press the “Stop” button;
• press the calculated letter within 10 seconds of pressing the “Stop” button.

The calculation consists of 6 iterations of the following procedure:

• Find the position of Input 1 in the grid. This is your first grid location.

In the first iteration, Input 1 is the letter from the small display.

For all other iterations, Input 1 is the previous iteration’s Result.

• Take the letter from the cycling sequence that corresponds to the current iteration. Its position in the grid is your second grid location.
• Calculate the distance from the first to the second grid location by counting squares in reading order. When reaching the end of a line, continue on the start of the next line. When reaching the end of the grid (bottom-right), continue from the beginning of the grid (top-left). If the grid locations are the same, the distance is 25.

For example, if the second grid location is immediately to the right of the first, the distance is 1. If the second grid location is immediately to the left of the first, the distance is 24.

• Shift Input 2 that many letters forward in the alphabet (with wraparound).

In the first iteration, Input 2 is the letter missing from the grid.

For all other iterations, Input 2 is the previous iteration’s Result.

If the shift results in the letter that was missing from the grid, perform the alphabetic shift by the same amount a second time.

This is the Result for this iteration.

The final calculated letter is the Result from the last iteration.