In article , Clive Coleman
writes
The first design of gate involved you walking through the gate while
it processed your ticket. At the end, you were either released with
your ticket or dumped into a "sin-bin" for an inspector to come over
and investigate.
I seem to remember the first ones had two sets of gates but the second
set only opened if your ticket was valid, thus trapping you,

I remember those, but that's not what I mean.

The design was an experiment that involved a walkway about 2 metres
long. It contained several metal bars like turnstile arms. You pushed
one in front of you, transporting your ticket along inside. If it was
valid, the arm dropped away to be carried back for re-use. If not, the
arm routed you into the sin-bin.

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