The video “How to use hidari-ba (left-blade) carving knives/scrapers (part 2),” which has been posted on the Netsuke Carving section, was recorded in 2012, that is eight years ago from now. (So were all the videos for beginners featuring hand saws, files, and hidari-ba tools.)
At that time my father was 78 years old. In the video he said he had a callus on the middle finger of his right hand. As you know, a callus is a part of the skin that has thickened and hardened as a response to repeated pressure. His callus was caused by the rod of the blade being pressed onto the middle finger when he carved with the hidari-ba.
My father used to work in the morning and afternoon, and sometimes also in the evening, nearly every day, for several hours in total. Now that he is 86 years old, he cannot work for such long hours. As a result, the callus has almost disappeared, he says. It is amazing how honestly the body reacts to daily activities.