# A wall that measures two different numbers

> A floor plan gives one measurement for a wall from outside and a different one from inside, and the gap has nowhere marked to go.

August 20, 2026 · https://justog.club/stories/the-room-that-measures-wrong

A floor plan of one room, drawn thin and precise in navy on pale blue. The walls run off two edges
of the print, cropped like a page from a working set of drawings.

Outside the top wall: 4.2m. Inside the same wall, in red: 3.6m.

## Why do two numbers on one wall feel wrong rather than simply mistaken?

Because both figures look like real measurements, taken properly, and a mistake this size doesn't
happen by accident in a trade built around getting it right.

A single wrong number reads as somebody's slip — a transposed digit, a tape read at the wrong end.
Two carefully drawn dimension lines, each labelled the way a real set of drawings labels them,
disagreeing by more than half a metre, reads as two separate, competent measurements that
genuinely don't agree. The print doesn't dramatise either number. It just states them both, in the
same clean hand, and lets a viewer notice that they can't both be true of the same wall.

## What exactly is drawn, and what isn't?

A rectangular room in thin outline, one dimension line outside the top wall reading 4.2m, a second
inside the same wall in red reading 3.6m, and nothing else marked anywhere on the sheet.

No section, no shading, no arrow pointing at where the difference might sit. The drawing gives a
reader exactly the two figures and the wall they both claim to describe, and stops. Six hundred
millimetres of something has to exist between an outside face reading 4.2 metres and an inside face
reading 3.6 metres on what's drawn as the same wall — the plan simply never says what, or where.

## What makes a good one?

A drafting register kept completely plain, so the two figures are the only thing doing any work.

Thin uniform line weight, a lettering style a real draughtsman would use, no cross-hatching, no
compass rose, nothing that reads as decoration. The red on the interior figure should be the only
colour in the whole print — a working convention for flagging a discrepancy on a real drawing,
repurposed here to mark the one number that doesn't belong. Add texture or shading anywhere else
and the sheet stops reading as a real technical drawing, which is the entire claim the print is
making.

## What's the rights position on printing an architectural drawing?

A floor plan drawn from scratch, of an invented room, belongs to whoever drew it — nobody is
licensing anything here because nothing here is copied.

Drafting conventions themselves — dimension lines, the small tick marks, the lettering style — are
shared technical vocabulary with no single owner, the same way musical notation belongs to nobody
in particular. A real architect's actual drawing of a real building is a different matter and
carries that architect's rights; this plan is invented for the print, room and numbers both.

## Does the same trick work on something other than a floor plan?

Any drawing that states its own measurements can carry the same disagreement.

A cross-section with two labelled depths that don't add up to the total given elsewhere on the
sheet. An elevation where a stated height doesn't match the number of storeys drawn above it. The
underlying fault is the same one that makes
[a house front's window count not add up against its width](/stories/the-wrong-number-of-windows)
work — a drawing that states enough of its own facts for a reader to check them against each other,
and finds they don't agree.

## Isn't six hundred millimetres just measuring error?

Six hundred millimetres is too large a gap for two careful measurements of the same wall to explain
as error, which is exactly why the drawing gives both figures rather than picking one.

A tape read from the wrong end, or a measurement taken to the wrong face of a stud wall, accounts
for centimetres, not the better part of a wall's thickness in a straight line. There are ordinary
explanations for a wall being thicker on one side than the numbers first suggest — a duct run
inside it, a chimney breast built into that face, a stud void deeper than it looks — and any one of
them could account for some of the difference. The plan names none of them and chooses none of
them. [A doorway whose surrounding brick doesn't match the wall it sits in](/stories/the-door-added-later)
works from the same refusal to say which explanation is the right one.

## Does it print well?

Yes — thin line work on a flat pale ground is about as forgiving as a print gets.

Navy on pale blue keeps the whole sheet in two tones, with red reserved entirely for the interior
dimension line so it reads instantly as the flagged figure rather than decoration. The lettering is
the risk: dimension numerals need to stay large enough to survive the weave at actual wearing
distance, the same problem
[a pair of angle labels that disagree with each other](/stories/eldritch-geometry-non-euclidean)
has to solve for its own numerals, or the whole discrepancy becomes illegible exactly where it needs
to be read.

## How do I get one made?

Describe the room at [JustOG](/) — its shape, where the two measurements sit, and how far apart the
numbers should land.
Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to
order and shipped.

Designs other people have published are in the [shop](/shop).

Both figures are correct, on their own terms, and the wall only has room for one of them to be true.