Context : The Galactic microquasar SS 433 is very luminous and launches oppositely-directed jets of cool hydrogen at a quarter of the speed of light .
Observations of emission lines from the circumbinary disk imply a system mass exceeding 40 M _ { \odot } , with the compact object exceeding 16 M _ { \odot } .
The most recent attempts to establish a mass via observation of absorption lines in the spectrum of the companion imply a system mass of less than 20 M _ { \odot } and a compact object of perhaps 4 M _ { \odot } .

Aims : To examine these conflicting data and present a possible resolution of this conflict .

Methods : Interpretation of data through the application of simple trigonometry to the configuration of the SS 433 system .

Results : The absorption spectra which , attributed to the atmosphere of the companion , yield an orbital speed of \sim 60 km s ^ { -1 } could well be attributable to absorption of light from the companion in material of the circumbinary disk .
Then the absorption spectra predict an orbital speed for the circumbinary disk material of \sim 240 km s ^ { -1 } , in agreement with the emission line data .

Conclusions : If continuum light from the companion is absorbed in passage through the circumbinary disk material rather than in the atmosphere of the companion itself , the periodic Doppler shifts in the absorption spectra are entirely consistent with observations of the circumbinary disk and a system mass exceeding \sim 40 M _ { \odot } .
The consistency is striking and the implication is that the compact object is a rather massive stellar black hole .