Let's see if we can compile a short database of numbers. I propose the distance from the tip of the nib to the center of mass as a measure of balance. I'll start with the two pen in my pocket right now (quick measurements, balancing the pens on each other, for which I estimate a 2mm precision) :
- Namiki Vanishing Point (nib out) : 7.0 cm (2.7'')
- Waterman Sérénité :
- non posted : 6.5 cm (2.5'')
- posted : 9.1 cm (3.5'')