Difficulty is about deduction, not size
Most puzzle games equate "bigger" with "harder." Lattice doesn't. A board's grade reflects how many linked steps of reasoning you need to solve it without guessing — the depth of the deduction chain, not the number of cells. A compact board that forces a long, single-threaded chain of inferences can earn a higher grade than a large one that falls apart into many easy, independent steps.
This is possible because the same engine that proves a puzzle is unique also measures how hard its unique solution is to reach. The grade you see is that measurement, not a human guess.
The five grades
Easy puzzles are mostly direct: scan for the equation with one unknown, fill it, repeat. The chain reaction does the work for you and rarely stalls.
Medium puzzles ask you to hold one or two facts in mind while you work, and to read operators as clues rather than just filling obvious blanks.
Hard puzzles introduce genuine forks where you must combine two separate clues — say, a product and a difference — to pin a single cell. The path is still forced, but it's no longer on the surface.
Expert puzzles demand longer chains and more careful tile-counting; you'll often prove what a cell can't be before you can prove what it is.
Master puzzles are deep: the decisive deduction may sit several inferences down a single thread, and seeing it is the entire challenge. Beating a Master board is a real accomplishment, because the engine has certified that the difficulty is honest.
Why honest grading matters
When difficulty is measured rather than guessed, the grade means something. A Master puzzle is hard for a concrete reason — the deduction is long — not because the board is cluttered or the timer is short. That lets you choose a challenge that fits your mood and trust that it'll deliver.
It also makes progress legible. As you climb from Easy to Master, you're not just doing more arithmetic; you're learning to see deeper chains of logic. The grades chart that growth.
Using the grades to improve
If you're new, stay in Easy and Medium until the cascade method feels automatic — until filling one cell and immediately spotting the next becomes a reflex. Then step up to Hard and start practicing the habit of forbidding candidates with operators.
When Expert feels comfortable, Master is mostly about patience: trusting that a forced answer exists and following the single thread far enough to find it. The daily puzzle is a good barometer — it's graded too, so you can feel your range widen over time.