Convert hectometer to roman perch

The in-between metric units are taught at school and then mostly forgotten – except regionally. Dutch motorways carry a 'hectometre post' every 100 m, so traffic news and breakdown services place a jam at 'A2, hectometre post 57.3'. In Sweden and Norway the decimetre is an everyday word, a half-decimetre being about two inches, and the decilitre does the same job in Nordic recipes. The decametre is the odd one out: 10 m is about the length of a bus, and the unit is hardly used anywhere.

Roman lengths were built on the foot (pes, about 29.6 cm): 16 digiti (finger widths) or 4 palmi (palm widths) made a foot, 1½ feet a cubit, 5 feet a passus (a double step), 10 feet a pertica (perch) and 120 feet an actus, the length of a furrow. Longer distances counted in stadia of 625 feet and in mille passuum, a thousand double steps or 5,000 feet, which is where the word mile comes from; the Gallic leuga was 1½ Roman miles. Milestones along the Roman roads were set one mille passuum apart.