diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index c10e3f5..a955393 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -1,6 +1,10 @@
 Changelog
 =================================================
 
+v1.9.1
+------
+*    centralize version number to a single place
+
 v1.9.0
 ------
 *    add beam_ellipticity()
diff --git a/docs/conf.py b/docs/conf.py
index fd19e34..89d545a 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -2,10 +2,23 @@
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 #
-import os
 import sys
+import os.path
 import sphinx_rtd_theme
 
+def read(rel_path):
+    here = os.path.abspath(os.path.dirname(__file__))
+    with open(os.path.join(here, rel_path), 'r', encoding='utf-8') as fp:
+        return fp.read()
+
+def get_version(rel_path):
+    for line in read(rel_path).splitlines():
+        if line.startswith('__version__'):
+            delim = '"' if '"' in line else "'"
+            return line.split(delim)[1]
+    else:
+        raise RuntimeError("Unable to find version string.")
+
 sys.path.insert(0, os.path.abspath('.'))
 sys.path.insert(0, os.path.abspath('..'))
 
@@ -15,9 +28,7 @@
 copyright = '2017-22, Scott Prahl'
 author = 'Scott Prahl'
 
-# The full version, including alpha/beta/rc tags
-release = '1.9.0'
-
+release = get_version("../laserbeamsize/__init__.py")
 master_doc = 'index'
 
 # -- General configuration ---------------------------------------------------
diff --git a/docs/sbfit.png b/docs/sbfit.png
index 0263ab9..5c3413b 100644
Binary files a/docs/sbfit.png and b/docs/sbfit.png differ
diff --git a/laserbeamsize/__init__.py b/laserbeamsize/__init__.py
index bb18a23..8728e4c 100644
--- a/laserbeamsize/__init__.py
+++ b/laserbeamsize/__init__.py
@@ -19,4 +19,4 @@
 from .laserbeamsize import *
 from .m2 import *
 
-__version__ = '1.9.0'
+__version__ = '1.9.1'
diff --git a/release.txt b/release.txt
index 07bbdd5..1179da2 100644
--- a/release.txt
+++ b/release.txt
@@ -5,10 +5,8 @@ Releasing a new version
 # check
   make rcheck
 
-# update the version in three different places!
-#           setup.cfg   docs/conf.py  laserbeamsize/__init__.py
-
-  git commit -m 'update version' setup.cfg docs/conf.py
+# update the version in __init__.py
+  git commit -m 'update version' laserbeamsize/__init__.py
 
 # update CHANGELOG.rst  `git shortlog v1.9.0..HEAD`
   git commit -m 'update recent changes' CHANGELOG.rst
diff --git a/sbfit.png b/sbfit.png
index 0263ab9..5c3413b 100644
Binary files a/sbfit.png and b/sbfit.png differ
diff --git a/setup.cfg b/setup.cfg
index ff8ad2e..fecce65 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,6 +1,5 @@
 [metadata]
 name = laserbeamsize
-version = 1.9.0
 author = Scott Prahl
 author_email = scott.prahl@oit.edu
 license = MIT
diff --git a/setup.py b/setup.py
index cb95015..accbf03 100644
--- a/setup.py
+++ b/setup.py
@@ -1,13 +1,21 @@
+import os.path
 from setuptools import setup
 
-# use README.rst as the long description
-# make sure to use the syntax that works in both ReST and markdown
-from os import path
-this_directory = path.abspath(path.dirname(__file__))
-with open(path.join(this_directory, 'README.rst'), encoding='utf-8') as f:
-    long_description = f.read()
+def read(rel_path):
+    here = os.path.abspath(os.path.dirname(__file__))
+    with open(os.path.join(here, rel_path), 'r', encoding='utf-8') as fp:
+        return fp.read()
+
+def get_version(rel_path):
+    for line in read(rel_path).splitlines():
+        if line.startswith('__version__'):
+            delim = '"' if '"' in line else "'"
+            return line.split(delim)[1]
+    else:
+        raise RuntimeError("Unable to find version string.")
 
 setup(
-    long_description=long_description,
-    long_description_content_type='text/x-rst'
+    long_description = read('README.rst'),
+    long_description_content_type = 'text/x-rst',
+    version = get_version("laserbeamsize/__init__.py")
 )