Example 25. John Baldwin In Nomine a4, mm. 1–8 (Audio: Fretwork 2019). The mensuration sign here () designates perfect semibreves (i.e., an undotted semibreve contains three minims rather than two) as can be seen in the cantus firmus in voice two. It also implies a metrical organization of the semibreve tactus being subdivided into three minims. This is, in fact, the metrical organization of the majority of this piece, though not the opening.