It indicates the motion or distance between upper a lower case letters on the typeface.
https://www.facebook.com/groups/olympiasg1/posts/1506621080656301/
also:
Greg Riutzel:<br /> That's how I see it. I measured it once. I put the ribbon in stencil, typed a lower case "h" and marked approx where the top of the type slug was on the paper. Then repeated with an upper case "H". The marks were just a tad over 7.5 mm apart checking with a rule. No precision of course but close.
The number printed on the ring in the basket of Olympia typewriters, just above and to the left of the word "De Luxe" is the distance from the baseline of the bottom slug character to the baseline of the top slug character.
In many instances it will be 7.6. I'm curious what other typefaces show and if this thesis holds?











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