THE CORE MECHANIC
Every clue is an arithmetic expression. Evaluate it to get the answer, then split the answer into individual digits and write one digit per cell in the run. A 3-cell run for the clue '12 × 7 = 84' would be wrong — 84 has only two digits but the run has three cells.
The run length and the digit count of the evaluated answer must match exactly. If they don't, you've either misread the clue, misidentified the run length, or made an arithmetic error.
EVALUATE BEFORE YOU WRITE
Work out the full arithmetic result before touching the grid. For multiplication and division, check your work — a mental-arithmetic slip on a clue like '23 × 17' fills the wrong digits and looks correct until the puzzle doesn't close.
- Addition and subtraction clues are usually fast. Write the result and split.
- Multiplication: decompose one factor if helpful (23 × 17 = 23 × 10 + 23 × 7 = 230 + 161 = 391).
- Division: verify the division is exact — Number Crossword clues always produce whole-number answers. If your division gives a remainder, recheck the clue.
THE NO-LEADING-ZERO RULE
Multi-cell runs represent multi-digit numbers. The first cell of any run cannot hold a zero — just like real numbers, 084 is not a valid three-digit answer (it's just 84, which would only fill a two-cell run).
If a clue evaluates to a result that begins with zero — which happens when the answer is smaller than the run expects — something is wrong: either the arithmetic, the clue reading, or the run boundary identification. Recheck before writing.
Tip: single-cell runs can hold any digit 0–9 including zero. Only multi-cell runs have the leading-zero restriction.
WORK FROM THE MOST CONSTRAINED RUNS
Since runs are independent (no down clues), there's no cascading constraint between intersecting answers. The only constraint is that each evaluated answer must exactly fill its run's cell count.
This means difficulty is purely arithmetic. Start with the clues you can evaluate fastest — simpler operations or numbers you recognise (squares, common multiples). Leave the harder mental-arithmetic clues for last, when you're warmed up.
CHECKING YOUR WORK
Because runs don't intersect, an arithmetic error in one run doesn't propagate — it just fills the wrong cells in that run. If you finish a run and the digits feel wrong, recalculate the clue from scratch rather than trying to spot the error in the filled digits.
A useful habit: for each clue, verify both that the arithmetic is correct AND that the digit count matches the run length before writing. Catching a mismatch before writing saves the erasing step.
THE BEGINNER MISTAKE
Filling digits in a run without checking whether the digit count matches the cell count. A 4-cell run filled with a 3-digit answer (say, writing '5', '4', '3' and leaving one cell blank) looks partially solved but is invalid. Count the cells in a run and the digits in your answer before writing anything.