while the soprano, alto, and tenor parts are notated in ¢. O is triple meter but at a higher tactus level than ¢, meaning that a breve here transcribes as a whole note rather than a half note. So, the first mensura (our modern day “measure” ought to be notated in 6/2 meter, equivalent to three measures of ¢. Similarly, a measure of C would be twice as long as a measure of ¢. The longa following the C section is in ¢ and so, like the other three voices is transcribed as a whole note. Immediately following that is a 2:1 proportion sign, followed a little later by a 4:1 proportion sign. After working out all the other parts, it becomes obvious that the 4:1 proportion following the 2:1 proportion cannot be cumulative, but instead refers back to ¢ which is the common mensural signature of the time. After working all this out, the bass voice becomes this: