Spectroscopic Binaries : the tilt problem
Mizar A : resolved by interferometry
Orbit face on : small effect                 Orbit edge on : big effect
One problem with spectroscopic binaries is that you can’t tell how badly the Doppler effect has been reduced by the orbital tilt. Fully face on orbits show no line-of-sight velocity at all. You get a lower limit to the sum of the masses (individual masses if both stars have visible spectral lines).