You turn the dial.
They feel the pin.
Five tumblers ride a ring. Five pins ride the plug. The door only gives when every pin stands at the shear line at the same rotation — and nobody can work that out alone. You can see the tumbler heights through the slit. Your partner, blind in the dark, can only tell you what one pin feels like at a time: up, jammed, or dead.
Name the pin, name the height, listen. The clock is the plant's and it does not care which of you is right.
The job waits.
The plant clock is stopped. Nothing on the other side of the door has moved.
The record reads method.
Five pins, nothing forced.
How the two of you talk.
DIAL turns the plug. Turning drops every raised pin, so the last rotation stands or falls as a unit. The plug over-travels more as the heat rises, and the window is the only thing that tells you it did.
LAMP is a shutter, not a torch. Held, it throws a wide sodium flood: turning costs half as much, and the whole window washes out. You get bands instead of heights and you lose the shape in the window, which is how you knew where you were. Released, the slit is narrow, exact and slow.
DOT sounds the pin at the top port, BAR the one at the bottom, HOOK braces both at once. The taller of the two heights must go on the matching wheel first: the wheels are how you tell your partner what the pin is up against. A wheel left on READ passes on whatever you can actually see — a number, or a band, or nothing.
Your partner answers UP, JAM or DOWN. UP means the pin stands proud of the gate. JAM means the gate grazes it by a hair — and a jam names the gate's height exactly, which is the one thing you cannot see from the inside. DOWN means it never moved. Say the wrong height and you poison their ledger; a ledger that closes to nothing is proof, and proof is all you get before a CALL.
A CALL against a standing proof costs you nothing but trust. A CALL against a clean ledger costs three beats, and a tired partner will remember it. Press the same signal twice at the same rotation and you are forcing a pin: that is a re-seat, and the third one re-locks the cylinder for the night.
The partner tires. A tired thumb shakes, mis-reports, and eventually leans on a pin that will not move — which is a re-seat you did not order. HOLD REST buys the thumb back and spends nothing but the clock.