DELTA is a pure logic puzzle on a thermal-color grid. Same-colored cells form regions, and each region's size equals the number it shows. Your only job is deduction.

THE RULE (you'll know it in 10 seconds):
Cells with the same value that share an edge form a region. Every region must contain exactly as many cells as the number it shows. Two regions of the same size can never touch. When the grid is correct, every number and every region agree.

CORE LOOP:
A handful of pre-filled cells seed the deduction. Tap a blank cell; pick a number from the thermal palette. Fill cells you can prove from existing values — never guess. Each placement repaints the cell in its thermal color and sometimes forces a neighbor's value, shown as a soft pulse. Cascading deductions feel inevitable once you see them.

PROGRESSION (all five tiers play on a 9×9 grid):
- Easy — 50% pre-filled. Single-step deductions, 1–3 minutes.
- Medium — 38% pre-filled. Overlapping constraints.
- Hard — 28% pre-filled. Multi-region forcing.
- Expert — 20% pre-filled. Two or three case-splits per puzzle.
- Master — 14% pre-filled. Endgame-level depth.

Unlock the next tier by completing 50 puzzles at the current one. The pacing is intentional: every tier teaches a habit the next one assumes you know.

KEY FEATURES:
★ ANALYZE — when you're stuck, a built-in solver flags every rule-violating cell in red so you can find the mistake without losing your place. Available as a premium hint.
★ Daily DELTA — one fresh puzzle every day, with a streak counter that tracks consecutive completions.
★ Multiple thermal palettes — the warm Thermal default, plus a Colorblind-Safe variant unlocked from day one. Pure visual choice; no gameplay change.
★ No subscription. Optional reward video for +1 hint. Prefer a quiet board? Remove ads with a one-time purchase — or go Premium for ads-off plus a stack of hints and every palette.
★ Plays offline. No account required. Local progress.

WHO IS THIS FOR:
If you love puzzles where the rule is short and the deduction is deep — Sudoku, Nonograms, Kakuro — DELTA gives you a single rule and a thermal landscape you'll learn to read at a glance. No narrative, no characters, no story-bloat. Just the grid, the rule, and the colors.

If you bounce off "guess and check" puzzles, you'll like that DELTA is built around proof. Every cell you fill is one you can justify before placing.

NEW TO LOGIC PUZZLES?
The tutorial walks through the region rule before you ever see your first puzzle. By the third Easy puzzle you'll be filling cells from sight, not from counting.

Count the heat.