User Guide

FontLab 4
184
Advanced Vertical Metrics
In TrueType font files vertical metrics can be stored in the OS/2 and hhea
tables. Different programs and operating systems use vertical metrics from
these tables. Windows usually uses data stored in the OS/2 table while the
Mac OS uses only data located in the hhea table.
It is important to correctly define all vertical metrics if you want your font
to align properly. In most cases FontLab can calculate vertical metrics
according to the system recommendations, but in some cases you may
want to customize these values.
We recommend you generally leave these values untouched in an existing
OpenType font. Of course, if you perform heavy modification of the font
you will need to update the advanced vertical metrics.
If you want FontLab to automatically calculate all vertical metrics, select
the option Calculate values automatically.
If you want to customize values, select the Set Custom values option and
edit data in the fields below. Note that if you choose Set Custom values but
leave all data unchanged, FontLab will restore the original vertical metrics
data from the imported font and the new updated font will align exactly as
the original one.