Yep, Castell math ruler allright... I saw it in your gallery; never saw it before ;-) Not the slightest idea what it is for... And even if you told me, I wouldn't understand a word, or letter, or number...

We do not see things as they are. ǝɹɐ ǝʍ sɐ sƃuıɥʇ ǝǝs ǝʍ