User Guide

Hinting
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Another possible application of the double link is hinting a character’s
middle horizontal stem:
Double link
If the position of the middle stem in different characters is different, you
cannot be sure that the hinted position will be the same at all PPMs, even if
the difference is very small. There is always a chance that at some PPM the
rounding of linked points will be different and the link will be shifted top
or bottom.
Be ready to set a number of middle delta instructions or, better yet, set a
special middle line alignment zone and use a combination of align and
single link instructions.