Stef wrote

for what is the px unit stand for? (from tex.stackexchange)

From the plain TeX reference: • pt: Point • pc: pica (12 pt) • in: inch (72.27 pt) • bp: Big point (72 bp = 1 in) • cm: Centimeter • mm: Millimeter • dd: Didot point • cc: cicero (12 dd) • sp: Scaled point (65536 sp = 1 pt), the smallest TeX unit • ex: Nominal x-height • em: Nominal m-width Available in math mode:

• mu: math unit, 1 em = 18 mu, where em is taken from the math symbols family, various lengths are derived from it (thinspace, thickspace, etc.) Additionally available in pdfTeX and LuaTeX: • px: "pixel", the dimension given to the \pdfpxdimen primitive; default value is 1 bp, corresponding to a pixel density of 72 dpi Stephan