the only way

Stumbled across John McCue's short article (with very nice sketch) for the BAA's Journal entitled "Observing Double Stars." His opening remark is intriguing:

Observing the time it takes for two stars to orbit each other in a binary system is still the only direct way to measure the mass of a star - knowledge that is central to the study [of stars].

He uses a stopwatch and calibrated eyepiece to measure doubles. He notes that one can use Aladin with their own photos and it will calculate the separation and position angle.