SCRUPLE

Nine sealed packets of metal. Each one is stamped with what it weighs. Exactly one of them is lying.

SCRUPLE is a real Game Boy cartridge — a 32,768-byte ROM you can put on a flash cart — containing forty assay problems. Play the first six free in your browser, right here on this page.

The balance tells you almost nothing

Every packet carries an assay mark: a wax disc with an engraved device and a row of punched pips that declares its weight in scruples. You can count them.

One packet’s true weight is a single scruple away from what its mark claims. The docket tells you whether it runs heavy, or light, or — on the harder cases — only that one of them is false.

The balance takes two marks a side and it says one thing: which way it tips. Never by how much.

So a weighing is a question, and the answer is the gap between what the marks declare and what the beam actually does:

These two declare five between them, and that one declares five. They should balance. They did not — so the liar is one of those three, and it is on the side that fell.

The docket grants the proved minimum, and not one more

Every case ships with the smallest number of weighings that can possibly identify the false mark, found by a complete search over every legal weighing the balance can perform — not a designer’s estimate, not a par score. Three outcomes per weighing means k weighings separate at most 3^k marks; the search proves whether that bound is reachable for that particular set of declared weights.

The docket bar grants exactly that number. A weighing spent badly cannot be bought back.

And the proof includes the instrument. Because the pans hold two marks each, some cases need three weighings that an unlimited balance would solve in two. That capacity is inside the search, so the number on the docket is always a number you can actually achieve. Every one of the forty cases has been played to a win on the cartridge by a bot following the proved-optimal line.

The declared weights are the puzzle

Nine identical packets would make every case the same case with the labels shuffled — the optimum would depend only on how many packets there are, you would learn one algorithm, and the cartridge would be over.

Because each mark declares a different weight, the arithmetic changes and so does the reasoning. Measured across two hundred generated problems: the declared-weight design produces 61 distinct optimal opening moves where identical packets produce 4.

What is in it

• 40 cases, trays of five to nine marks, from two-weighing dockets to three
• 172 distinct assay marks drawn across them. Fifteen authored device silhouettes and three modifiers, composed by the generator into a wax disc with an engraved rim, a cast shadow and a punched tally that states the number. There is no sprite sheet in the ROM
• A proved minimum on every case, with the balance’s own capacity inside the proof
• A verdict that shows its working — the false mark, what it declared, and what it really weighed
• Game Boy sound-hardware audio: no samples, no files
• A free browser demo of the first six cases, on this page, playable now

Controls

d-pad move the calipers · A left pan · B right pan · START weigh · SELECT clear the balance, and when it is already empty, name the false mark

The bottom of the screen always says what the buttons do right now.

Honest notes

It has not been run on physical hardware by us. It is driven frame by frame on binjgb, which is a very good emulator and is not a Game Boy. The ROM is a valid DMG cartridge — the Nintendo logo and the header checksum the boot ROM enforces are checked on every build — but we are not going to claim a hardware test we did not do.

This is an AI-built product and it is tagged as one. Code and graphics are AI-written. The sound is the Game Boy’s own four channels driven by register writes — no samples, no audio files, no generative-audio model.

More Game Boy cartridges from CSAF

WARDLOCK · WITNESS MARK · PROOFMARK · ANATOMIST · the whole catalogue