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Comment by efm | Hacker News Reader

What mechanism did the Selectric use?

"When the typist presses a key, a pawl on the key lever depresses a matching metal bar (interposer) for that key. The interposer, which is oriented front to back in the machine, has one or more short projections (lugs) protruding from its bottom edge. Each interposer has a unique combination of lugs, corresponding to the binary code for the desired character. Each interposer also has a tab that slots in between loose steel balls in a race, the size of balls and race selected precisely to leave a total gap barely larger than the width of the interposer tab, such that only one interposer tab can fit in the free space and thus only one letter can be selected at a time." [1][2]

Not exactly comparable to the one on a modern PC, I guess.

[1] https://en.wikipedia.org/wiki/IBM_Selectric_typewriter#Selec...

[2] https://www.youtube.com/watch?v=uTjxwVfx8GA

The Selectric feel was particularly good in a few ways:

- it had a very light pre-pre-travel of a millimetre or so, providing distinct touching-but-not-pressing feedback;

- the force drop at the tactile snap point was so high it felt like the keyboard was actively trying to help you type;

- the post-travel was long and gradual enough that even an aggressive operator like me wouldn't normally bottom out.

IBM beam springs got part of the way by using two springs (one of them two-piece). Another spring or two, or some nonlinear springs, could probably do better.

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