A lot of careful design and construction went into these old units. [Linked Image]

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I used to teach my students how to lace using waxed cotton. {.....} I myself was trained by old brittish post office engineers so everything had to be exact.
I don't know about these days, but how to lace-up a wiring loom with waxed cotton was still on the PO/BT training schedule in the mid-1980s.