I recently discovered a curious feature in a font called Raleway. Some of the glyphs for decimal digits ( 0 - 9 ) are placed above or below the baseline. Numbers displayed using the font seem to be wavy rather than straight. I'm wondering if this is done to make the digits easier to distinguish from each other. Is that the only reason or are there other reasons behind diverting the digit glyphs from baseline? What is the name of this feature?
They are called old style numerals. Typically a good open type font has an option to choose between old style or not. At the same time you can choose between tabular options too. But not all fonts make all combinations so like in the case of the Raleway i have installed they are has no tabular alternates.
Image 1: Oldstyle vs Lining. Note: Propotional and tabular are the same for Raleway Medium
But if we take a more complete font like Myriad Pro we get a better picture of what the tabular lining fonts do. They make the numbers and in certain cases punctuation, monospaced so that they line up.
Image 2: Myriad Pro actually has a tabular lining number variant too.
In adobe applications you can find this under open type settings window of the font.