For my first experience in wood turning, I decided to complete a pen. I first did studies of people holding pens, in order to understand what would be the best ergonomic fit. I asked friends, who all had varying experiences in their pen use (range 1-10 hours a day), and took into account their experiences in determining the shape of the pen.
The final shape I decided on minimizes fatigue, reducing cramping of the thumb and index finger. Additionally, the density of the material, as well as the weight of the remaining wood is such that it has enough heft to write with the pressure of gravity, but not so much that the weight increases fatigue.