@costello - that does sound like a sign of stress, although is it possible that it sooths him? I guess it depends on how intrusive it is or becomes. Like finding new mathematical calculations is a hobby the way others might enjoy crochet, or model trains, or raising chickens.... . If it is something he can go over in his mind for awhile to create calmness - great. If it becomes an all consuming passion - maybe bad. I will hope for the former.