True, but a 31 knotted rope would be unwieldy, not?

Here are some Medieval measurements from various regions:
English:
Digit: 3/4"
barleycorn, about 1/3", originally based on the length of a grain of barley
ynch, or inch: 3 barleycorn
nail: 3 digits
palm: 3 inches
hand: 4 inches
span (width of outstrentched hand from tip of thumb to tip of little finger): 3 palms
foot: originally 13 inches, shortened to 12 after 1066 to base it on the Roman foot.
cubit: 18 inches
ell: 20 nails or 45 inches
yard (after 1066): 3 feet
fathom (distance from one fingertip to the other on outstretched arms): 6 feet
rod: uncertain original length, defined as 16 1/2 feet after 1066

French:

pied: 12 pounce
pounce: 12 ligne
ligne: about 2.2558 mm

German:

Rute: varied, 0, 12, 14, 15, 18 or 20 feet
Klafter: Fathom, usually 6 feet, although in can range to as high as 3 meters in Switzerland
Elle: Distance between elbow and finger tip. In the North often 2 feet, In Prussia 17 / 8 feet, in the South often 2 1/2 feet.
Fuss: foot, varied by region
Zoll: inch, 1/12 of a foot, sometimes 1/10th of a foot.
Linie: 1/12 or 1/10 of a foot

Norwegian:

alen: Forearm, varies locally
fot: foot, 1/2 alen
kvarter: quarter, 1/4 alen
tomme: thumb, inch. 1/12 foot
linje: line, 1/12 tomme
steinkast: stone's throw. approximate measure, perhaps 25 favner
stang: rod, 5 alen
skrupel: 1/12 linje