# The overlap where two projectors share one picture

> A timeline bar with two cue points and two overlapping rectangles is a diagram of the only moment the audience's picture depends on two machines running at once.

August 21, 2026 · https://justog.club/stories/four-seconds-to-change-over

A bar, split into four. Two small circles above it, near either end. Below, two long rectangles
that almost meet — except for one short stretch where they overlap.

Nothing on it is labelled, and everything on it is a schedule.

## What does the diagram actually show?

Two machines handing a picture to each other without a visible join.

One projector is running a reel; a second projector, already loaded and warmed up, is standing by.
For a short stretch near the end of the first reel, both machines run at once — the second one
picking up the picture while the first one is still projecting it — and then the first shuts down.
The bar is the timeline of that handover. The overlap is the only part of the whole schedule where
two machines are doing the job simultaneously.

Everywhere else on the bar, exactly one projector is running. The overlap is deliberately the
smallest part of it.

## Why two circles rather than one?

Because the handover needs two separate instructions, seconds apart, done by the same person.

The first circle marks the point where a projectionist starts the second machine. The second marks
the point where the first machine is closed down and the picture on screen has fully passed to the
new reel. One cue without the other leaves either two pictures overlapping on the screen, or a gap
with no picture on it at all. [The mark that carries each of those
cues](/stories/the-cue-dot-in-the-corner) is tiny and easy to miss on purpose — the diagram
here is the two-part instruction it triggers, drawn at the scale the job actually happens at.

## Why is there nothing written on the bar?

Because the sequence is the information, not any specific number.

Four seconds, two projectors and two cues describe the shape of the job in any booth running any
reel — put a number on the bar and it stops being a general description and starts being a claim
about one particular room's equipment. Leaving it unlabelled is what lets the same diagram describe
the job everywhere it's still done.

## Can I use a diagram like this freely?

Yes — a timing diagram of a standard procedure isn't authored artwork, it's closer to a wiring
schematic. Nobody owns the shape of two overlapping rectangles on a bar.

What would need permission is a diagram redrawn from a specific manufacturer's manual, with that
manufacturer's own labelling and house style reproduced exactly. A generic bar with no branding and
no numbers on it, like this one, isn't tracing anybody's proprietary drawing.

## Is this a print for one person or two?

It reads well as a pair — one projectionist in the first rectangle's ink, a colleague or a partner
in the second, both wearing the same bar.

It's one of the few diagrams here where the shirt still makes sense worn alone: the whole point of
the overlap is that, for four seconds, two people are doing one job together, and a single wearer
can stand for either half of that. It sits alongside [a card of cues for the room's
lighting](/stories/the-house-lights-on-a-cue) as the same kind of instruction, aimed at the
same booth, for a different part of the show.

## Isn't four seconds too short to matter?

That's exactly the size of the job, and the diagram is built to make a short window look like the
event it actually is.

Four seconds is long enough for two irreversible actions and short enough that almost nobody in the
seats notices it happening. The audience's experience of a continuous film across the whole running
time rests entirely on that short overlap going right, every time — which is a larger claim than
the window's length suggests, not a smaller one. [The running order the projector is serving comes
from a sheet decided in advance](/stories/the-trailers-in-a-fixed-order), but the changeover
itself happens in real time, with nothing to fall back on if it's late.

## Does it print well?

Very well — it's a diagram built from flat rectangles and hard ticks, which is exactly what
survives printing best.

Keep the bar's segments crisp rather than shaded, the two circles small and solid, and the overlap
in one contrasting ink against the two rectangles' base colour. Fine gradients would blur the one
detail that matters — where the overlap actually starts and ends — so there shouldn't be any.

Slate, ink blue or charcoal grounds suit it. Two inks: one for the bar and rectangles, one for the
overlap and the two circles.

## How do I get one made?

Describe the handover at [JustOG](/) — how long the overlap reads, where the two cue points sit,
which projector's ink goes where. 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).

For four seconds, two machines are running the same film, and then only one of them is.