Units of Measurement

Mensa Ponderaria

The public office for weights and measures was located very close to the little fruit and vegatable market (Forum Holitorium), close to Pompeii's main Forum and next to the east wall of the Temple of Apollo (VII.7.31).
The standard for calibration was the local Oscan metric system. As declared by the inscription on the façade, it was later changed to conform to the system introduced by Augustus.
The machine consisted of two overlapping limestone benches - only the lower one is present here; each with a cavity corresponding to the different measures and a hole at the bottom for the item under measure to be pushed through.
The inscription (around 20 BCE) reads: Aulus Clodius Flaccus son of Aulus, Numerius Arcaeus Arellianus son of Numerius, Duovirs with the power of law, gave this by the decree of the Decurians for the measures to be equaled out (CIL X.793).


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%