STEP 1 — EVALUATE EVERY CLUE BEFORE PLACING ANYTHING
Work through every arithmetic clue and compute the answer. Write the answers beside the clues, not in the grid yet. This pass is arithmetic only — no placement decisions. Doing it first prevents the common mistake of placing a plausible-looking number that doesn't actually match the clue.
If a clue involves multiplication or division, do that step explicitly: '12 × 7' is 84, not 87. Arithmetic slips at this stage are the single largest source of errors in Number Crossword.
STEP 2 — MATCH DIGIT COUNT TO RUN LENGTH
Each answer must fill its run exactly — one digit per cell. A 2-cell run needs a 2-digit answer (10–99). A 3-cell run needs a 3-digit answer (100–999). If your computed answer has the wrong digit count, you made an arithmetic error — recompute before placing.
This check catches most errors before they spread. A 1-digit answer in a 2-cell run is always wrong; use it as an immediate alarm.
STEP 3 — APPLY NO-LEADING-ZERO RULE
Multi-digit numbers don't start with 0. If your answer is 07, the run requires at least 2 cells but you have a leading zero — that means the clue result is actually 7 (a 1-digit answer), so the run must be 1 cell long, or you've made an arithmetic error. Check the clue again.
For runs that start in the first cell of a row, this constraint is automatic. For interior runs, it's a useful sanity check on borderline answers.
STEP 4 — START WITH THE MOST CONSTRAINED RUNS
"Most constrained" means the run whose answer has the fewest digit arrangements: a 2-cell run narrows the answer to a 2-digit number; a clue like '100 ÷ 10' gives exactly 10, a single answer. Start with runs where the answer is uniquely determined and spans a short run — they place with no ambiguity.
Runs where the clue is a simple product or quotient are usually more constrained than sums — fewer valid answers fit a given run length.
STEP 5 — USE SHARED CELLS BETWEEN RUNS
When two runs share a cell, the digit in that cell must satisfy both runs. After placing one run, read the shared-cell digit and verify it is consistent with the intersecting run's expected digit in that position. Conflicts flag an arithmetic error in one of the two runs.
Number Crossword has no down clues, so shared-cell logic comes from the grid structure itself: a cell at the end of one run that is also the start of a crossing run is a natural verification point.
SOLVING ORDER
- Evaluate all clues (arithmetic only).
- Check digit count versus run length for each.
- Apply no-leading-zero check.
- Place the most constrained runs (shortest and/or uniquely determined).
- Use shared cells to verify adjacent runs.
- Repeat until solved.
BEGINNER TRAP — PLACING BEFORE EVALUATING
The most common mistake is guessing a plausible-looking number into the grid before computing the clue exactly. '8 × 9' looks like it could be 63 or 81 — but it's 72. Always evaluate first, place second. The grid gives you no feedback on arithmetic errors; the only check is your own calculation.