This is the ultimate pen. There have been many others but there can only be One. This is
it. Of the few I’ve used, the M4B Military Version is my favorite edition. It has served me for years in north Africa, China, Patagonia, Tierra del Fuego, Greenland and other inhospitable places. As the advertisement says, it can write from -30 deg F to 250 deg F without problem, as well as underwater, upside down and through grease. I’ve tested 3 of the specifications and found them to be solid.