Units of length

According to the original definiton of the metre, the meridional circumference of the Earth should be 40 000 000 m. The real value is greater. Hexapotamian segesimal system is based on the value 40 007 520 m, Optaquan octal system is based on the value 40 007 620.362 24 m.

segesimal system

40 007 520 m = meridional circumference
6 667 920 m = meridional sextant
666 792 m
111 132 m = meridional degree
11 113.2 m = double league = 2 hours of walking
1852.2 m = bass mile = meridional minute
185.22 m = (sharp baryton) stadion = 2 minutes of walking
30.87 m = (sharp subbaryton) plethron = meridional second
3.087 m = (flat baryton) perch = 2 seconds of walking
514.5 mm = flat subbaryton cubit = meridional third
51.45 mm = subtenor nail
8.575 mm = barleycorn = meridional fourth

octal system

40 007 620,362 24 m = meridional circumference
6 667 936.727 04 m = meridional sextant
833 492,090 88 m
104 186,511 36 m = meridional octal degree
13 023.313 92 m
1627,91424.2 m = subtenor mile = meridional octal minute
203.489 28 m = subtenor stadium
25.436 16 m = subtenor plethron = meridional second
3.179 52 m = subtenor perch
397.44 mm = subtenor cubit = meridional octal third
49.68 mm = subtenor nail
6.21 mm = wheatcorn

comparison of systems

	Optaquan	metric	English	Hexapotamian
wheatcorn (G-corn)	6.21 mm	6.25 mm	6.35 mm	6.431 25 mm	¼″
barleycorn (D-corn)	8.28 mm	8⅓ mm	8.46 mm	8.575 mm	⅓″
c-finger	18.63 mm	18.75 mm	19.05 mm	19.293 75 mm	¾″
H-finger	19.872 mm	20 mm	20.32 mm	20.58 mm	⅘″
thumb (G-finger)	24.84 mm	25 mm	25.4 mm	25.725 mm	1″
G-nail	49.68 mm	50 mm	50.8 mm	51.45 mm	2″
(F-)nail		56.25 mm	57.15 mm	57.881 25 mm	2¼″
palm (c-hand)	74.52 mm	75 mm		77.175 mm	3″	¼′
(G-)hand	55.89 mm	100 mm		102.9 mm	4″	⅓′
(G-)span	55.89 mm	200 mm		205.8 mm	8″	⅔′
head		225 mm		231.525 mm	9″	¾′
foot	298.08 mm	300 mm		308.7 mm	12″	1′
palmipes	372.6 mm	375 mm			15″	1¼′
(F-)cubit	447.12 mm	450 mm		463.05 mm	18″	1½′
(As-)gradus	745.2 mm	750 mm		771.75 mm	30″	2½′
yard		900 mm		926.1 m	36″	3′
(As-)passus	1.4904 m	1.5 m		1.5435 m	60″	5′
fathom		1.8 m		1.8522 m	72″	6′
(As-)perch	2.9808 m	3 m		3.087 m	120″	10′
(E-)knot		15 m		15.435 m	600″	50′
Des-chain		18 m			720″	60′
(E-)plethron		30 m		30.87 m		100′
(A-)stadion		180 m		185.22 m		600′
(As-)stadium	186.3 m	187.5 m				625′
As-mile	1490.4 m	1500 m		1543.5 m		5000′
F-mile		1800 m		1852.2 m		6000′
(Hes-)league		5400 m		5556.6 m		18000′

aliases

wheatcorn = G-corn = subtenor corn (¼ of a thumb)
barleycorn = D-corn (⅓ of a thumb)
thumb = G-finger = subternor finger = big finger
third = Es-cubit = subbaryton cubit (20 thumbs)
head = F-span = bass span (9 thumbs)
yard = F-gradus = bass gradus (36 thumbs)
fathom = F-passus = bass passus (72 thumbs)

A third is pars minuta tertia, third small part of the meridional degree, but per chance also one third of a (flat baryton) passus.