bug#31702:

[Carlos Pita]

Ok, I think I now understand the problem a bit better:

1. Changing the height from 102 to 109 sets the effective height to
105. This size is the same of that of the font which both the font
select dialog and gnome-terminal show for "Hack 11" (I have counted
pixel by pixel in comparative xmag shots).

2. From 110 to 116 the effective size is 113 as stated above. This is
the size corresponding to "Hack 12" in the font selector and in
gnome-terminal.

3. 117 rounds up to 120, etc.

So I guess it's just a different way of rounding up to the next
available size (I don't know which is the precision of the underlying
font renderer but I assume it's not a tenth of a point... from the
numbers above it seems to be about 6 or 7 tenths of a point).

But:

* The fact that setting the font from the font dialog offered in the
menu bar of emacs itself doesn't set a font with the height that was
previewed in the dialog is a bit disturbing.

* Besides, since the height attribute documentation explicitly states
that the it is measured in tenths of a point, the rendering of a font
with height P * 10 in emacs should exactly match the rendering of the
same font with size P in the system. There is no "rounding up" excuse
for the mismatch between 110 and 11, for example.