FEM: constants, more exact values

src/Mod/Fem/femtest/data/calculix/thermomech_flow1D.inp

@@ -134,7 +134,7 @@ Eedges
 ** written by write_constraints_selfweight function
 ** ConstraintSelfWeight
 *DLOAD
-Eall,GRAV,9820,0.0,0.0,-1.0
+Eall,GRAV,9806,0.0,0.0,-1.0
 
 
 ***********************************************************

src/Mod/Fem/femtools/constants.py

@@ -33,20 +33,24 @@ __url__ = "http://www.freecadweb.org"
 
 
 def gravity():
-    return "9.82 m/s^2"
+    # https://en.wikipedia.org/wiki/Gravitational_acceleration
+    return "9.80665 m/s^2"
 
 
 def stefan_boltzmann():
-    return "5.67e-8 W/(m^2*K^4)"
+    # https://en.wikipedia.org/wiki/Stefan–Boltzmann_constant
+    return "5.67037e-8 W/(m^2*K^4)"
 
 
 def vacuum_permittivity():
     # https://forum.freecadweb.org/viewtopic.php?f=18&p=400959#p400959
-    return "8.8542e-12 s^4*A^2 / (m^3*kg)"
+    # https://en.wikipedia.org/wiki/Permittivity#Vacuum_permittivity
+    return "8.85419e-12 s^4*A^2 / (m^3*kg)"
 
 
 def boltzmann_constant():
-    return "1.3807e-23 J/K"
+    # https://en.wikipedia.org/wiki/Boltzmann_constant
+    return "1.38065e-23 J/K"
 
 
 """