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.
Improve this question
$\endgroup$
2
  • $\begingroup$ Look at the subscripts: it's attribution of portions of the total error to different effects $\endgroup$
    – Carl Witthoft
    Apr 10, 2019 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, 2019 at 18:57

1 Answer 1

Reset to default
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
$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .