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Lining tnum in italic shape

mauro sacchettomauro sacchetto Posts: 353
edited March 2021 in Font Technology
Generally, in roman shape tabular digits (lining tnum) are realized centering the glyphs into a fixed lenght, the same one for all. This way, left and right bearing are symmetric for each glyph.
But: for italic shape? Which is the requested technic? In the most part of fonts, I see the same total space,but an asymmetric bearing...
Thank you!
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    George ThomasGeorge Thomas Posts: 633
    Probably because the outlines need to be shifted in order that the italic will fit well when used within the roman.
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    mauro sacchettomauro sacchetto Posts: 353
    Let me understand better, please.
    Generally, if you are using tabular numbers, they do not fit into text. In this case, proportional numbers, lining or old style, are better used.
    Moreover, I do not understand the logic of creating certainly irregular tabular figures due to a totally uncertain proximity to a Roman text ...

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    Igor PetrovicIgor Petrovic Posts: 263
    edited March 2021
    I would not say that any set of figures (proportional/tabular/lining/old style) usually have the same values for left and right side bearing (if that's what you mean). Not in roman nor in italic. 

    No matter which advanced width figures take the goal is to make them "look" centered on that width, which usually means different SB values.

    Or you would like to say that tabular figures in italic don't even look centered?
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    John HudsonJohn Hudson Posts: 2,977
    Don’t assume that tabular numbers are only used in tables, or that tables do not include text. Consider, e.g. spreadsheets, which may contain combinations of text and numbers, in which it is likely, for convenience that tabular numerals will be use everywhere, regardless of whether a cell contains a number or a mix of text and number.

    So the spacing and offset of tabular italic numeral glyphs needs to coordinate with the spacing and offset of all the other italic glyphs, and you also want words or numbers in italics to be spaced correctly between non-italic words (which will, in turn, mean that vertical columns of italic and non-italic numbers will align nicely).

    To achieve this, the best method is to define a fixed measurement height for sidebearings, somewhere around the middle of the x-height, and use that across the entire family of all styles and weights.
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