[jack_jennings]

Hi Rasmus, I think that at the point size at which this is meant to be used—e.g. around 11px (https://rsms.me/interface/lab/?size=11&compare=roboto) —the differences between the two become harder to distinguish. The issue is really that the character of the type is going to be dictated by the systematic decisions: stroke weight, x-height, proportion, spacing. Starting from Roboto and not changing these parameters in your solution means drastically limiting how far away from the original source that you can realistically get. In the end, changing the stroke endings and changing the bounding box of some characters in invisible in the intended use case.

Here is a screenshot comparing Roboto (11.5px) to InterfaceRSMS (11px), which illustrates: http://imgur.com/a/nl5mp

There are plenty of UI typefaces out there that take a noticeably different approach, an easy comparison to Lucida Grande is probably enough to justify the point. (EDIT: for completeness, http://imgur.com/a/CjD06)

[rasmusfabbe]

Thanks for the thoughtful comment. Indeed really small sizes like 11px, distinguishing factors are few and even San Francisco and Roboto start looking like the same font, at least as far as most people are concerned. The goal with Interface is not to create a unique-looking typeface, or even to try to make something different in terms of style, but to create the best possible small-size, computer-screen, user-interface oriented font, even if that means that some characteristics become very similar to other typefaces. For instance.

[jack_jennings]

My argument is only that starting with the proportion and metrics of Roboto and not changing them means that what you will end up with at best is a marginal improvment over Roboto. If "marinal improvement over Roboto" is what you are aiming for, great, but don't oversell it or your work will be dismissed in the same way that I did in the original post. There are myriad solutions to how letterforms are created, and it isn't a foregone conclusion that these forms are or will continue to be "the best".

[davidad_]

FWIW, I do find Interface to be subjectively noticeably more pleasant than Roboto in the comparison here.

[jack_jennings]

The comparison is not great for objective comparison—the metrics of Interface have been changed so that 11px =/= 11px from one to the other… this was the best approximation that I could get in-browser. Usually you'd want to set the two typefaces up so that the x-height is the same, and in this case Roboto is probably slightly larger still, and hence a bit darker in overall color.

[rasmusfabbe]

Actually, I think you want to compare apples & apples, meaning Font A and Font B at the same size and line height.

[jack_jennings]

Except that isn't how font metrics work—the size of the type on the body is not necessarily equivalent between two different fonts. There is no stanard that says that 12pt Times shares any vertical metrics with 12pt Helvetica, or 12pt anything else.

The most informed comparision can be made when the x-height is optically equivalent. The other option, cap height, isn't as useful because it is then harder to judge the lowercase (a majority of the letterforms).

[nonissue]

I think what jack's saying is that "font-size" to some extent is arbitrary. It's not scientific or worthwhile to compare fonts across a specific size if they have different x-heights. The only meaningful comparison is to evaluate legibility for fonts that are "relatively" the same size. For example, if Interface 12pt is equivalent in x-height to Roboto at 12.5pt, and Roboto is more legible, and legibility is the goal, then obviously the user should pick Roboto at 12.5pt (all things considered).

[lucaspiller]

Also subjective, but at that size on my machine (13" MBA, non-Retina, El Capitan, Chrome), I find Roboto is a lot easier to read. Interface looks 'greyer' and the contrast isn't so good.

[TuringTest]

While not the intended use case, I find Interface to be surprisingly readable at extremely tiny font sizes (7, 6, and even 5!).

Sure, you shouldn't be designing an interface with those sizes, but it may be something to consider for some zooming interfaces (primarily maps with lots of tags: street names, POIs, etc.)

[brusch64]

For me it was the other way round. Roboto was much more compact and easier to read. Interface seemed to use more whitespace in the words.