My old man who is 70 wears reading glasses except when he goes out to eat (can't read a menu) or fishing. He's not tech savvy and still uses a flip phone because he can talk to Captain Kirk. I've been fishing in 20-40 feet of water which would be ideal for him to use electronics. I use my boats 5 inch fishfinder and he can see it, but I don't think he would navigate the menus to fine tune it. A fishfinder may be too complex with all the buttons and menus to operate. Is it safe assume with a flasher he could see green and red lines move around the circle without glasses? Maybe a FL 8?