-const string FGJSBBase::needed_cfg_version = "1.60";
-const string FGJSBBase::JSBSim_version = "0.9.4";
+
+// Note that definition of lbtoslug by the inverse of slugtolb and not
+// to a different constant you can also get from some tables will make
+// lbtoslug*slugtolb == 1 up to the magnitude of roundoff. So converting from
+// slug to lb and back will yield to the original value you started with up
+// to the magnitude of roundoff.
+// Taken from units gnu commandline tool
+const double FGJSBBase::slugtolb = 32.174049;
+const double FGJSBBase::lbtoslug = 1.0/slugtolb;
+
+const string FGJSBBase::needed_cfg_version = "1.61";
+const string FGJSBBase::JSBSim_version = "0.9.5";