UltraPrecision

Note   UltraPrecision fonts have an UPM grid of 3333 by 3333 units. The UPM (Units Per eM) is the number of units that defines the coordinate grid on which the characters of a font are drawn. The bigger the UPM grid is, the more coordinate space there is, and the more precise the characters can be drawn. PostScript (Type 1) fonts have an UPM grid of 1000 by 1000 units. PostScript flavored OpenType fonts usually have the same UPM grid of 1000 by 1000 units (= 1,000,000 grid points). TrueType fonts and TrueType flavored OpenType fonts usually have an UPM grid of 2048 by 2048 units (= 4,194,304 grid points). UltraPrecision fonts have an UPM grid of 3333 by 3333 units (= 11,108,889 grid points). The extra precision which is offered by UltraPrecision fonts, is based on these differences in UPM units.

Historical Note   The PostScript Type 1 and TrueType font technologies are around for quite some time now. PostScript Type 1 has been introduced in the mid-1980’s, and TrueType has been introduced in the beginning of the 1990’s. With the introduction of OpenType in 1996, a font specification arrived which uses either PostScript or TrueType outlines inside a ‘wrapper’. Although the OpenType specification adds a lot to those two original font specifications, it still does include the outline specification of those two older font formats.
       The traditional UPM grid of PostScript Type 1 and TrueType fonts made sense in the 1980’s and in the beginning of the 1990’s — because of the limitations of the hardware of that time. Since then, those limitations have disappeared — but the traditional UPM grid of PostScript Type 1 and TrueType still exists today in most OpenType fonts. However, the specification of both PostScript Type 1 and TrueType does support a bigger UPM grid than the traditional 1000 by 1000 and 2048 by 2048 grids, respectively.
       UltraPrecision fonts utilize a bigger UPM grid than fonts which follow the tradition of either the 1000 by 1000 or 2048 by 2048 grid. The UPM grid of UltraPrecision fonts is 3333 by 3333 units — which is within the limitations of both the PostScript Type 1 and TrueType grid specifications (so it is also within the limitations of the OpenType specification).