[EN] SI to fur/ftn (units & values)

(defconstant fur (* 220 3 12 254/100 1/100)

  "A furlong, 220 yards (m).")

(defconstant ftn (* 14 24 3600)

  "A fortnight (s).")

(defun fur/ftn (v)

  "Convert m/s to furlong/fortnight.

Exactly for an exact argument."

  (/ v (/ fur ftn)))

(fur/ftn 1) ;unit

6.012885e+3

(let ((u (/ fur ftn)))

  `(,(float u) ,(fur/ftn u))) ;unit

(1.6630952e-4 1)

(fur/ftn (/ 5e3 3600)) ;typical human walking

8.351229e+3

(fur/ftn (* 7.6 1852 1/3600)) ;typical WW2 U-boot (submerged)

2.3509045e+4

(fur/ftn (* 17.7 1852 1/3600)) ;typical WW2 U-boot (surface)

5.475133e+4

(fur/ftn (/ 120e3 3600)) ;typical speed limit (divided highway)

2.0042948e+5

(fur/ftn 335) ;typical Mach 1: standard day, sea level (NASA; 1100 ft/s)

2.0143164e+6

(fur/ftn 11.186e3) ;Earth escape velocity

6.726013e+7

(fur/ftn 299792458) ;light

1.8026175e+12

See also:

<https://en.wikipedia.org/wiki/FFF_system>

_________

The above was produced with the help of the following (something of a rarity where casual use of EVAL is more or less warranted):

(with-open-file (out "/storage/emulated/0/Documents/fur-ftn.txt" :direction :output :if-exists :supersede)

  (loop with *print-case* = ':downcase

    for x in '(

((fur/ftn 1)

 "unit")

((let ((u (/ fur ftn)))

  `(,(float u) ,(fur/ftn u)))

 "unit")

((fur/ftn (/ 5e3 3600))

 "typical human walking")

((fur/ftn (* 7.6 1852 1/3600))

 "typical WW2 U-boot (submerged)")

((fur/ftn (* 17.7 1852 1/3600))

 "typical WW2 U-boot (surface)")

((fur/ftn (/ 120e3 3600))

 "typical speed limit (divided highway)")

((fur/ftn 335)

 "typical Mach 1: standard day, sea level (NASA; 1100 ft/s)")

((fur/ftn 11.186e3)

 "Earth escape velocity")

((fur/ftn 299792458)

 "light")

)

  do

  (format out "~S ;~A~%~E~%"

                       (first x)

                       (second x)

                       (eval (first x)))))