Vertically aligned figures colon

Has anyone heard of a vertically aligned colon for lining figures and how it would be implemented? I’m thinking specifically in terms for use in times such as 09:54am…

San Francisco has it. I haven’t had a chance yet to look at the font, but I what I would do is just call it colon.lf, and Glyphs can automatically put it into the lnum feature.

Wait a minute, I am not so sure this makes sense, because it should only be replaced between two lining figures. So, calt is the better place after all:

sub @LiningFigure colon' @LiningFigure by colon.lining;
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Exactly what piqued my curiosity.

Very clever!

I ask myself whether this is too arcane to be deserving of its own unicode slot…

I think that would be better put in a stylistic set.

I thought you might like to know I discovered the ratio glyph: http://www.fileformat.info/info/unicode/char/2236/index.htm

FWIW, SF has the colon in a few places: a stylistic set, some special feature, and calt.

The SS and misc feature are simply – sub colon by colon.case;
The calt is:
sub @1-9 colon’ @1-9 by colon.case;
@A-Z colon’ @1-9 by colon.case;
@1-9 colon’ @A-Z by colon.case;

Also it’s really only A-Z, doesn’t apply for accented capitals.

I think that is pretty bad because it should only appear when exactly two figures follow, and at least one figure is before.

Why there is a substitution if a letter follows or precedes, I do not understand. But that is just me bitching, who knows what they had in mind.

I tried to do it with the following lookup in the calt feature.

lookup colonsub {
sub @figures @figures @figures colon’ @figures by colon;
sub @figures @figures colon’ @figures @figures @figures by colon;
sub @figures @figures colon’ @figures @figures by colon.calt;
sub @figures @figures colon’ @figures by colon;
sub @figures colon’ @figures @figures @figures by colon;
sub @figures colon’ @figures @figures by colon.calt;
sub @figures colon’ @figures by colon;
} colonsub;

It seems to work fine but I am not very experienced with programming substitutions. Do you think there are any issues with this approach?

Is there a point to all of the lines which substitute colon by colon?

As mekkablue suggested it should only substitute the following cases: 0:00 and 00:00 so I am not sure if it is the right way to do it, but the point is to exclude all of the other cases (like 0:0, 0:000+, 00:0, 00:000+, 000+:0).

Assuming one doesn’t make use of the ratio glyph then these substitutions make sense when representing scale, in say an ordinance survey map.

Isn’t the ratio intended to be used in cases such as the ordnance survey map? If one doesn’t make use of it then yes, the calt substitution shouldn’t exclude these other occurrences. My intention was to use it just for time.