Try writing the same short message in two different number systems. One person can use alphabet positions while another uses a grid, then they can compare answers. The two cards below both start with READ MAP: one uses A1Z26 and the other a Polybius square.
Choose the reference before writing the card
Give each card the chart its reader needs. A1Z26 numbers tell you a letter’s place in the alphabet; Polybius numbers tell you its row and column. For instance, 15 means O in A1Z26 but E in this Polybius square. A clear method label saves the reader from guessing which meaning you intended.
Make the two clue cards
Card A: alphabet positions
READ MAPA1Z26; A = 1; hyphens between letters; / between words18-5-1-4 / 13-1-16Card B: grid coordinates
READ MAPFixed I/J square; row first; spaces separate tokens42 15 11 14 32 11 35| Card | What to print beside it | Expected prepared answer |
|---|---|---|
| A | A = 1 through Z = 26; / marks a word boundary | READ MAP |
| B | The 5 × 5 I/J square; first digit is row | READMAP |
The Polybius tool removes the space before encoding, so its exact decoded answer is READMAP. If you want learners to restore READ MAP, give them two answer boxes or the word lengths as an extra clue. The coordinates themselves do not preserve that space.
Use this exact coordinate chart
| Row / column | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| 1 | A | B | C | D | E |
| 2 | F | G | H | I / J | K |
| 3 | L | M | N | O | P |
| 4 | Q | R | S | T | U |
| 5 | V | W | X | Y | Z |
I and J share a cell in this chart. Keep the same chart throughout the activity; a Tap Code square, for example, combines C/K instead. For a first card, a message without J lets learners focus on finding coordinates. Later, try JOIN and discuss why its prepared form is IOIN.
Let each reader take their time
- Let the reader choose a number card or a grid card.
- Work through the first token together and say what each number means.
- Give enough blank space to record one letter at a time.
- Compare the full answer only after all tokens have been read.
- Swap card types and ask which reference made the rule easier to understand.
There is no need to make this a race. If a letter does not fit, go back to its number or coordinate and look it up together. Keep the answers on another sheet so the cards can work for independent practice as well as a shared activity.
Check before making more copies
Decode both clues with the matching tools before printing more copies. Check the hyphens and slash on Card A and every two-digit pair on Card B. For more grid practice, create a Polybius worksheet, save its seed, and keep its answer pages separate.