This thread is inspired by confusion in another thread which may be due to a Wikipedia article, I consder misleading and muddled, about the observer effect, https://www.scienceforums.net/topic/116760-observer-effect-and-uncertainty-principle-are-the-same/ although I would say it has relevence to several other current threads as well.     https://en.wikipedia.org/wiki/Observer_effect_(physics)   Now I think it is good to separate out errors of measurement due