Hanayama levels, from 1 to 6

Level 1 and 2: learning the vocabulary.

These come apart in anywhere from two minutes to half an hour. They are not trivial, they are teaching pieces: each one contains exactly one idea, usually a rotation that lines up two gaps. Start here even if you think you are above it.

Level 3: the first real evening.

Three moves deep instead of one. A level 3 is where people discover that cast puzzles reward putting the thing down and picking it up an hour later with fresh eyes.

Level 4: the honest middle.

A long evening or several short ones. Level 4 pieces tend to have a move that feels wrong right up until it works, which is why they are the grade most often bought twice as a gift.

Level 5: weeks, not hours.

At this grade the solution has a sequence long enough that you cannot hold it in your head. Solvers start leaving a level 5 on the desk and turning it over between other tasks.

Level 6: the shelf of honor.

Six is reserved for a handful of designs. They have defeated people who solve everything else quickly, and the honest advice is to own one before you can solve it, because the month of carrying it around is the product.

Never force a cast puzzle.

Across every grade the rule holds: the solution is never strength. If a piece needs pressure you have the wrong orientation, and a forced cast puzzle picks up scratches that never come out.