I've recently purchased an unspecified pelikan pen, with purple cap and piston knob. judging by the size, it could be a m250 or an m400, since it has a 585 gold nib with Pelikan logo. It has one goldplated ring between the barrel and the piston knob. the gold plated ring on the cap reads "Germany", "Pelikan". the ink window seems to be blueish. I wish I could post a picture, but my phone was stolen and i have no way to take one until i get a new one. do you know how i could determine whether it is a M250 or an M400?