Units of Measurement

Distance
Digitus Finger 1/16 foot 1,848 cm
Unica Inch 1/12 foot 2,464 cm
Palmus Hand 1/4 foot 7,392 cm
Semis   1/2 foot 14,785
Pes (Roman) Foot 1 foot 29,57 cm
Palmines Palm-foot 1 1/4 feet 36,96 cm
Cubitus Cubit 1 1/2 feet 44,36 cm
Gradus Pace 2 1/2 feet 73,93 cm
Passus Double pace 5 feet 1,478 m
Actus Furrow 120 feet 35,48 m
Mille passus (Roman) mile 5000 feet 1478,5 m

Distance between manholes (putei)
Vitruvius 8.4.3 1 actus (120 Rf) 35,48 m
Plinius NH 31.31 2 actus (240 Rf) 70,96 m
Burdy Gier aqueduct   72 - 77 m

Gradient
Vitruvius 8.6.1 1/2 foot to 100 feet 0,5% (5 promille)
Plinius NH 31.57 1/4 unica to 100 feet 0,02 % (0,2 promille)
Mean   0,15 - 0,30%