Because views may have differing X and Y scales this size can only make sense in one of these directions otherwise text would appear warped on these kinds of views. The X direction was chosen to represent the font size. For instance if the X scale is 1 unit/mm and my Y scale is 2 units/mm a font size of 3.0 view units will result in un-rotated text that appears 6 view units or 3mm high in the Y direction. Another important thing to keep in mind that this size represents what is known as the "ascent" height of the font. The full height of the text may be higher if characters with accents or lower extension (e.g. the lowercase y) appear in the text. For TrueType fonts the mapping system will do a best effort positioning and sizing of the text using the alignment set and information about the font that it queries from the operating system. For instance; if Arial text "Blog" is placed at (0,0) and the alignment setting is Left-Bottom the left side of the B should be aligned at 0 in the X direction and the bottom of all the letters except y will be at 0 in the Y direction. The lower part of the y will extend below 0 in the Y (this is known as the "descent" height of the font at this size). The letters B and l should be very close to the size set here (this may differ slightly for different fonts).

public void TextSize(
	double d1
)

Public Sub TextSize ( 
	d1 As Double
)

public:
void TextSize(
	double d1
)

member TextSize : 
        d1 : float -> unit