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[AV Media Matters] Why 19 inch?

It's a serious question and one that I cannot answer. The
question is: when
was the standard for rack-mounted equipment introduced and why was it 19"
wide and in units of 1 3/4" tall?

The earliest documented record I have encountered is a description of
telephone repeater station equipment dated 1919 (IPOEE Journal).
The chances
are that this came from Western Electric Ltd, which would
indicate that 19"
was a Western Electric (and perhaps Bell System) standard.

But does anyone have chapter and verse?

Incidentally, the old chestnut linking it to the width of jackfields on
manual telephone swithcboards doesn't have much credibility. For a start,
they are not built on 19" frames.

Andy Emmerson.

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