provide some more explanation for the predefined constants

Author: Vindaar

src/unchained/constants.nim

@@ -5,20 +5,38 @@ import si_units, units
 ## in the units of Unchained.
 
 const
+  ## The speed of light in vacuum.
   c* = 299792458.0.Meter•Second⁻¹
+  ## The vacuum permitivity / electric constant.
   ε_0* = 8.8541878128e-12.A•s•V⁻¹•m⁻¹
+  ## Charge of an electron.
   e* = 1.602176634e-19.C
+  ## Mass of an electron.
   m_e* = 9.1093837015e-31.kg
   m_e_c2* = 0.510998928.MeV
+  ## Mass of a muon.
+  m_μ* = 1.883531627e-28.kg # 105.6583755e3 # MeV / c²
+  m_μ_eV* = 105.6583755e6.eV # / c²
+  ## The Avogadro constant. The number of particles in one mole of substance, per definition.
   N_A* = 6.02214076e23.mol⁻¹
+  ## The 'molar mass constant'. Prior to redefinition in 2019 it was defined as exactly
+  ## M_u = 1 g/mol. It relates the standard atomic weight of an element with its
+  ## mas for one mole of substance.
   M_u* = 0.99999999965e-3.kg•mol⁻¹
+  ## The 'atomic mass constant', the "base mass" for atomic scale objects, defined as
+  ## `m_u = 1/12 · m(¹²C) = 1 Dalton`
+  ## i.e. the average mass of a single nucleon in a bound atom.
   m_u* = M_u / N_A
-  m_μ_eV* = 105.6583755e6.eV # / c²
-  m_μ* = 1.883531627e-28.kg # 105.6583755e3 # MeV / c²
   π* = PI
-  r_e* = e*e / (4 * π * ε_0 * m_e * c * c) # classical electron radius
+  ## The classical electron radius.
+  r_e* = e*e / (4 * π * ε_0 * m_e * c * c)
   #K = 4 * π * N_A * r_e * r_e * m_e_c2 * (100.0^2)# [MeV mol⁻¹ cm²]
+  ## The Boltzmann constant
   k_B* = 1.380649e-23.Joule•Kelvin⁻¹
+  ## Planck's constant
   hp* = 6.62607015e-34.Joule•Hertz⁻¹
+  ## Reduced Planck's constant
   hp_bar* = hp / (2 * π)
+  ## Newton's constant. Note: We do not use the common variabl `G`, as it obviously conflicts
+  ## with the `Giga` prefix in the general case. Feel free to locally define it as such.
   G_Newton* = 6.6743e-11.N•m²•kg⁻²