Recreating Gerstner's The Tangential Eccentric (1956/1957), made with Python in @drawbotapp.
Gerstner: ‘The onlooker changes the picture according to his disposition and mood … He shares the fun and also the responsibility.’ (Designing Programmes, pp 78, 79)
Maybe this onlooker wasn’t who Gerstner had in mind, but I think he’d approve.