In LaTeX, you can easily change the font size, using the
\fontsize macro (described here) followed by the
\selectfont macro. But what is this font size? I changed the font size using the code
Mx, and then printed it on my laser printed. I then measured the width of the
M and the height of the
x; these measured turned out to be approximately 6.9 cm and 3.9 cm, respectively. So none of these turned out to be 10 cm. Not even the diagonal of the
M measured 10 cm, even if it wasn't far from it; this measured 9.4 cm.
I then printed the text
lql, drew a straight line between the tops of the two
ls, and measured the distance from the bottom of the
q to the line I had just drawn, thinking that this distance might turn out to be 10 cm. Nope. Only 8.2 cm.
So what measure is it that is 10 cm, that is, where in the text do I find the font size? I want to know this because I need to adjust the vertical distance between the lowest descender and the highest ascender to 0.5 cm on a text I'm going to have at the spine of a book.