User Guide

FontLab 4
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Me t r i c s and Di m e nsi o ns
This page is used to set font dimensions that are used mostly to properly
align text lines.
Font UPM Value
The most important field on this page is the Font UPM. Let’s explain what
UPM is and why it is so important.
The UPM (Units Per eM) is the basis of all font dimensions. The UPM is
the number of font units that defines the font height and the coordinate
grid on which the glyphs are drawn.
The bigger the UPM is the more coordinate space you have, so you can set
more precise positions of points. For technical reasons in FontLab the
UPM is limited to 10000 units, but we strongly recommend you work with
one of the standard UPMs. In Type 1 fonts the standard UPM is 1000 units
and in TrueType fonts the UPM may be set to any value, but the
recommended value is 2048 units.
If you change the UPM value in the Dimensions page of the Font Info
dialog box this doesn’t necessarily mean that the size of the characters will
change. For example, if you change the UPM from 1000 to 2000 all the
glyphs will now be half as big as they were before – because they are still
dimensioned at 1000 UPM. You have to scale all the characters to fit them
in the new UPM setting manually or you can switch on the Scale all
characters according to UPM change check box and all the font data will
be scaled automatically.