Good Morning Rose: The Railroad pen is a double ruling pen. The ruling pen had a hollow handle to allow the pen to swivel freely, it was used to drawing curvilinear lines, like contours on a map. The railroad pen would draw parallel lines of equal and or unequal width. It was trial and error, set the points, drop in some ink, draw a line, let it dry and then compare the width of the line to line guide to see if it was the correct width. You turned a little adjusting wheel to make it wider or narrower. The railroad pen had to ruling pens in a single handle, each one independently adjusted and only rarely were the same width the first time you tried. Practice made perfect or at least the ability to produce reasonably accurate maps or drawings in my case. Drafting and cartography were interesting and I did enjoy them up to a certain point. :-)