diff --git a/rpn/makeHelp.py b/rpn/makeHelp.py
index 06c5950..7cb3a7e 100644
--- a/rpn/makeHelp.py
+++ b/rpn/makeHelp.py
@@ -6321,7 +6321,7 @@ def makeCommandExample( command, indent=0, slow=False ):
 of the electric and magnetic fields of electromagnetic radiation travelling
 through free  space. That is, z_0 = |E|/|H|, where |E| is the electric field
 strength and |H| is the magnetic field strength.  Its presently accepted value
-is z_0 = 376.730313668(57) ohms.
+is z_0 = 376.730313412 ohms.
 ''',
 '''
 ''' + makeCommandExample( 'vacuum_impedance' ),
@@ -7831,11 +7831,11 @@ def makeCommandExample( command, indent=0, slow=False ):
 '''
 c:\\>rpn _dump_constants
 aa_battery:  15400 joule
-alpha_particle_mass:  6.644657230e-27 kilogram
+alpha_particle_mass:  6.6446573450e-27 kilogram
 april:  4
 august:  8
-avogadro_number:  6.022140756e23
-bohr_radius:  5.29177210903e-11 meter
+avogadro_number:  6.02214076e23
+bohr_radius:  5.29177210544e-11 meter
 ...
 ''',
 [ '_dump_cache', '_dump_conversions', '_dump_operators', '_dump_stats', '_dump_units',
diff --git a/rpn/units/rpnConstantOperators.py b/rpn/units/rpnConstantOperators.py
index 9f263fb..fc9a3fe 100644
--- a/rpn/units/rpnConstantOperators.py
+++ b/rpn/units/rpnConstantOperators.py
@@ -52,7 +52,7 @@
 ''' ),
 
     'bohr_radius' :
-        RPNConstantInfo( '5.29177210903e-11', 'meter', [ ], False,
+        RPNConstantInfo( '5.29177210544e-11', 'meter', [ ], False,
                          'the Bohr radius, an idealized measure of the size of a hydrogen atom',
                          '''
 From https://en.wikipedia.org/wiki/Bohr_radius:
@@ -66,7 +66,7 @@
 ''' ),
 
     'classical_electron_radius' :
-        RPNConstantInfo( '2.8179403227e-15', 'meter', [ 'electron_radius' ], False,
+        RPNConstantInfo( '2.8179403205e-15', 'meter', [ 'electron_radius' ], False,
                          'the classical size of an electron',
                          '''
 Ref:  https://en.wikipedia.org/wiki/Classical_electron_radius
@@ -80,7 +80,7 @@
 ''' ),
 
     'electric_constant' :
-        RPNConstantInfo( '8.8541878128e-12', 'ampere^2*second^4/kilogram*meter^3',
+        RPNConstantInfo( '8.8541878188e-12', 'ampere^2*second^4/kilogram*meter^3',
                          [ 'e0', 'e_0', 'e_nought', 'e_sub_0', 'free_space_permittivity',
                            'vacuum_permittivity' ], False,
                          'the permittivity of free space',
@@ -126,7 +126,7 @@
 ''' ),
 
     'magnetic_constant' :
-        RPNConstantInfo( '1.25663706212e-6', 'newton/ampere^2',
+        RPNConstantInfo( '1.25663706127e-6', 'newton/ampere^2',
                          [ 'free_space_permeability', 'mu0', 'mu_0', 'mu_sub_0', 'mu_nought' ], False,
                          'the permeability of free space',
                          '''
@@ -183,7 +183,7 @@
 ''' ),
 
     'nuclear_magneton' :
-        RPNConstantInfo( '5.0507837461e-27', 'joule/tesla', [ ], False,
+        RPNConstantInfo( '5.0507837393e-27', 'joule/tesla', [ ], False,
                          'the nuclear magneton, a physical constant of magnetic moment',
                          '''
 From https://en.wikipedia.org/wiki/Nuclear_magneton:
@@ -296,7 +296,7 @@
 
     # subatomic particle constants
     'alpha_particle_mass' :
-        RPNConstantInfo( '6.644657230e-27', 'kilogram', [ ], True,
+        RPNConstantInfo( '6.6446573450e-27', 'kilogram', [ ], True,
                          'the mass of an alpha particle (helium nucleus)',
                          '''
 The alpha particle is the equivalent of a helium nucleus, and consists of two
@@ -314,7 +314,7 @@
 ''' ),
 
     'electron_mass' :
-        RPNConstantInfo( '9.10938356e-31', 'kilogram', [ 'electron_rest_mass' ], True,
+        RPNConstantInfo( '9.1093837139e-31', 'kilogram', [ 'electron_rest_mass' ], True,
                          'the mass of the electron',
                          '''
 The electron rest mass is the mass of a stationary electron, also known as the
@@ -356,7 +356,7 @@
 ''' ),
 
     'neutron_mass' :
-        RPNConstantInfo( '1.674927471e-27', 'kilogram', [ ], True,
+        RPNConstantInfo( '1.67492750056e-27', 'kilogram', [ ], True,
                          'the mass of a neutron',
                          '''
 The neutron is a subatomic particle, with no net electric charge and a mass
@@ -370,7 +370,7 @@
 ''' ),
 
     'proton_mass' :
-        RPNConstantInfo( '1.672621898e-27', 'kilogram', [ ], True,
+        RPNConstantInfo( '1.67262192595e-27', 'kilogram', [ ], True,
                          'the mass of a proton',
                          '''
 A proton is a subatomic particle with a positive electric charge of +1
diff --git a/rpn/units/rpnEstimates.py b/rpn/units/rpnEstimates.py
index fcad90a..b8f3603 100644
--- a/rpn/units/rpnEstimates.py
+++ b/rpn/units/rpnEstimates.py
@@ -1085,7 +1085,7 @@
     mpmathify( '1.0e-17' )        : 'the range of the weak force',
     mpmathify( '8.5e-16' )        : 'the approximate radius of a proton',
     mpmathify( '1.5e-15' )        : 'the size of an 11 MeV proton',
-    mpmathify( '2.81794e-15' )    : 'the classical electron radius',
+    mpmathify( '2.8179403205e-15' )    : 'the classical electron radius',
     mpmathify( '1.0e-12' )        : 'the longest wavelength of gamma rays',
     mpmathify( '2.4e-12' )        : 'the Compton wavelength of electron',
     mpmathify( '5.0e-12' )        : 'the wavelength of shortest X-rays',
diff --git a/rpn/units/rpnUnits.py b/rpn/units/rpnUnits.py
index 6059b72..401c499 100644
--- a/rpn/units/rpnUnits.py
+++ b/rpn/units/rpnUnits.py
@@ -6622,7 +6622,7 @@
     ( 'blintz',                     'gram' )                                : mpmathify( '36.42538631' ),
     ( 'carat',                      'grain' )                               : fadd( 3, fdiv( 1, 6 ) ),
     ( 'chandrasekhar_limit',        'gram' )                                : mpmathify( '2.765e33' ),
-    ( 'dalton',                     'gram' )                                : mpmathify( '1.66053906660e-24' ),  # based on best measurements
+    ( 'dalton',                     'gram' )                                : mpmathify( '1.66053906892e-24' ),  # based on best measurements
     ( 'doppelzentner',              'zentner' )                             : mpmathify( '2' ),
     ( 'fortnight',                  'day' )                                 : mpmathify( '14' ),
     ( 'funt',                       'dolya' )                               : mpmathify( '9216' ),