1
$\begingroup$

As far as I know, the plus-or-minus sign is used to indicate the statistical margin of error of a measurement. But what does it mean when there are two plus-or-minus signs in the same measurement?

Some examples from Wikipedia:

  • The mass of M87* is given as (6.5 ± 0.2stat ± 0.7sys) × 109 M☉ (as measured by the Event Horizon Telescope).
  • The measured distance to Sagittarius A* is given as 7860 ± 140 ± 40 pc.
$\endgroup$
  • $\begingroup$ Look at the subscripts: it's attribution of portions of the total error to different effects $\endgroup$ – Carl Witthoft Apr 10 '19 at 17:57
  • 1
    $\begingroup$ Hm. So are the different portions additive? e.g. could you say that the distance to Sgr A* is 7860 ± 180 pc? $\endgroup$ – ahiijny Apr 10 '19 at 18:57
3
$\begingroup$

The first error is due to the precision of the measurement, the second is an uncertainty associated with methodology used.

| improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.