The properties specify the font height.
property Size: Integer;
property SizeDouble: Integer;
(SizeDouble is introduced in version 15)
Size specifies the font size in points, similarly to TFont.Size.
SizeDouble specifies the font size in half-points, i.e. its value is twice greater than Size.
Assigning to one of these properties changes value another one. SizeDouble allows to specify a font size with higher precision.