How to interpret error of absolute magnitude of a star given data from wikipedia? This Wikipedia page contains information about the star Spica in the rightmost table. A small snapshot of this table is below.



In this table, the absolute magnitude is given as −3.55 (−3.5/−1.5). Instead of seeing the value and error given as value ± error, I am thinking the error is given as it is because of absolute magnitude is given on a logarithmic scale (as opposed to linear scale). But I am not quite sure how to interpret this as an error reading. How does one interpret this reading?
Spica (&alpha; Vir) is a binary star.
The Wikipedia article cites Herbison-Evans et al. 1971, whose Table III says:


  Absolute magnitude of primary (Mv1) &nbsp; -3.5&plusmn;0.1
  Absolute magnitude of secondary (Mv2) &nbsp; -1.5&plusmn;0.2


So the confusing "-3.55 (-3.5 / -1.5)" can be interpreted as "combined (primary / secondary)."