What it measures

Clearance: The board in the cavity, tried at 0 and at 90 degrees. The gap on each side is measured against the 1.0 mm a side the check asks for.
Depth: Standoff height plus board thickness plus the tallest part, against the depth of the cavity.
Mounting holes: Every hole at least 2.0 mm across must sit within 0.5 mm of a standoff center, and the standoff's pilot hole must be smaller than the board hole, so a screw bites.
Connector openings: Each connector needs an opening on its own edge, centered within 0.75 mm, at least the catalog size for that connector.

When the board only fits turned 90 degrees, the report says so and runs every other check in that orientation.

Which checks your files get

What the check can measure depends on where the board and the case came from. A line it cannot measure is stamped NOT VERIFIED, never left blank.

Fit checks by board source and case source
Board	Case	Clearance	Stack height	Mounting holes	Connector openings
Designer	Designer	Measured	Measured	Measured	Measured
Designer	STEP	Estimate	Estimate	Not verified	Not verified
Designer	STL	Outside size only	Not run	Not verified	Not verified
Board file	Designer	Measured	Not verified	Measured	Not run
Board file	STEP	Estimate	Not verified	Not verified	Not run
Board file	STL	Outside size only	Not run	Not verified	Not run

Not verifiedThe check runs and the report says it cannot see this. Check it by hand.
Not runThe check does not run for this pair.

What the check can measure

It depends on where the board and the case came from. Only a board and a case both made in the designer get all four checks.

Board file: an uploaded kicad_pcb or Gerber outline, or a board saved from the tscircuit board editor. If a project has one, the check uses it instead of a board in the designer. Likewise, an uploaded STL or STEP replaces a case in the designer.
Measured: exact geometry. Clearance, stack height, and connector openings can PASS, WARN, or FAIL. Mounting holes can PASS or WARN only. A tight clearance, a mounting hole off its standoff, or an undersized opening is a WARN, not a FAIL.
Stack height counts the standoff, the board, and the tallest connector only. Other parts are not modeled.
Estimate: measured against an interior estimated from an assumed 2.0 mm wall. For stack height, standoffs count as zero. The report marks it as an estimate.
Outside size only: the board is compared with the outside of the case. The line can FAIL, never PASS.
Not verified: the report says the check cannot see it. Check it by hand.
Not run: the check does not run for this pair.

The stamp on each line

Pass: Measured, and inside the limit.
Warn: Measured, and it works, but it is tighter than asked or smaller than the catalog size. Read the line and decide.
Fail: Measured, and it does not work as drawn. Change the design or the case before you order.
Not verified: The file cannot show this, so it was not measured. Confirm it by hand, or draw the part in the studio so it can be.

Every stamp is a glyph and a word, so a report reads the same printed in gray or seen without color.

Every finding the check can return

Each line of a report carries one of these findings, with its own sentence and, where there is one, the measured number beside the required one.

Fit check findings, the stamp each one carries, and what it means
Finding	Stamp	What it means
Board fits with clearance	Pass	The gap on every side is at least the gap asked for.
Clearance is tight	Warn	The board fits, with less gap than asked on at least one side.
Board does not fit the cavity	Fail	The board is larger than the cavity at 0 and at 90 degrees.
Interior unknown	Not verified	The case is a mesh, so only its outer box is known.
Depth is enough	Pass	Standoffs, board and tallest part fit under the lid.
Not enough depth	Fail	The stack is taller than the cavity is deep.
Depth not checked	Not verified	The height of the tallest part or the board thickness is unknown.
Mounting holes line up	Pass	Every mounting hole sits on a standoff.
Hole has no standoff	Warn	A mounting hole has no standoff close enough. The line gives the distance to the nearest one.
Pilot hole too large	Warn	A screw through the board hole would not bite into the standoff.
Mounting not verified	Not verified	The case was uploaded, so the standoff positions are unknown.
Connector cutouts line up	Pass	Every connector has its opening, centered and at least catalog size.
Wall cutout missing	Fail	No opening is centered on the connector closely enough. The line says how far off the nearest one is.
Wall cutout is undersized	Warn	The opening is in place but smaller than the catalog size, so the plug may not seat.
Cutouts not verified	Not verified	The case was uploaded, so its wall openings cannot be seen.
Board design lint	Warn	A rule the studio checks on its own boards did not hold. The line says which.

The verdict

A report fails when any line fails. It fits with warnings when no line fails and at least one line is WARN or NOT VERIFIED. It fits only when every line passes. The report states the verdict at the top, in words.

Reading a report, line by line

Start with any FAIL. Its sentence says what is wrong and by how much.
Then each WARN. Many are fine to accept; the measured and the required numbers let you decide.
Then each NOT VERIFIED. Each one names what to confirm by hand.
Change the design or the case, then run a new fit check. Every run is kept on the project, so you can compare them.

Running one, and what it costs

Start a fit check from the project. It costs $19.00 a run. The check runs right after you confirm it, on the board and the case saved in the project at that moment, and the report is saved on the project, where you can read it in full.

What things cost

What it does not check

The circuit, the firmware, or whether the board works. The check measures geometry.
Heat, sealing or certification.
More than one board in one case. The check measures one.