If we measure a number, we get an interval. What if we measure a function or an operator?

摘要

Assume that we measure a physical quantityxwith a measuring device whose accuracy isδ(i.e., whose producers guarantee that the difference$$x--bar x$$between the actual valuexand the measured value$$bar x$$does not exceedδ). If the result of this measurement is$$bar x$$, then possible values ofxform an interval$$bar x - delta ,bar x + delta $