Hello. So one of the axioms of measurement science is that every measurement we make is an approximation and can never reflect the true magnitude of a physical phenomena. We would then go on to teach that there is a certain "true" magnitude which is something that experts or majority would agree represents that particular physical phenomena "best" Then one would define absolute error as being: [tex] \left | Measured magnitude - Expected/"true" \right |[/tex] How is this expected/ "true" value arrived at? I can understand theoretically by calculations one might get some ideal number but in real life due to instruments not working properly or precision limitations, are there any other examples? Also is it correct to say accuracy is the reproducibility of the measured quantity through repeated measurements? how does one measure accuracy? through statistics I imagine. Are there any examples where people do not "agree" on the "true" value of a measure? eg some constant in physics?