Theodor Kovàcs is a mysterious historical figure, particularly for someone who had such a profound impact upon the history of fountain pen development. There is surprisingly little written about him and his work outside of what Pelikan Schreibgeräte and its derivatives tell us. His birth, family, activities outside of Pelikan, and death are all questions that I have been unable to answer despite extensive research. Much of what we do know seems to be based upon a strong oral history as well as a scant trail of patents and corporate agreements. A great deal of this history, I have already put forth in my piece, Where It All Started: The Transparent Pelikan Fountain Pen so please forgive any redundancy. While I have previously dedicated time to the fruits of Mr. Kovàcs’ labor and partnership with Günther Wagner, I have never taken a deep dive into the engineering behind the differential piston mechanism that has become a defining characteristic of Pelikan’s 90+ year fountain pen legacy. Not just an incremental improvement, Mr. Kovàcs’ designs were evolutionary, taking the potential of these analogue instruments to the next level. I thought that it might be enlightening, particularly for the more engineering minded amongst us, to peek behind the curtain and see what makes a Pelikan tick, at least as it did back in the early days. The designs that follow are derived from the original patents filed by Mr. Kovàcs and Günther Wagner back in the 1920s which ultimately became the linchpin behind the company’s fountain pen fortunes. All the illustrations below have been annotated according to the patent’s text for ease of viewing. Of course, there have been some small improvements to the piston design over the past nine decades, but the fundamentals remain the same. Read on to learn how Pelikan’s differential piston filling mechanism got its start.