This article is very clear, comprehensively explaining the process of the ballpoint pen from its initial conception to its widespread adoption.

What I find most interesting is that it wasn't a single person's breakthrough, but rather a process of decades of continuous iteration—from its early use only on leather to its later transformation into an everyday tool thanks to advancements in ink and manufacturing processes. This process of maturing through a combination of technology, materials, and manufacturing processes is quite typical.

The section about British pilots using it at high altitudes is also interesting; it seems many everyday items initially had rather "extreme" applications.

I'm a little curious, when you were compiling this information, which stage did you consider most crucial? Was it the improvement in ink, or the breakthrough in precision manufacturing?