diff --git a/README b/README
index 9ccb0e43343138a293cfbb994f7b5bef2373e314..759d61715eac15788694b89fc68ea9ef85085091 100644
--- a/README
+++ b/README
@@ -1 +1,20 @@
 InstallSystems Next Generation
+
+INSTALLSYSTEMS VERSIONNING
+__________________________
+
+A valid version is an integer without dot.
+A version n, may be followed by a ~, to indicate it's inferior to n
+A version n, may be followed by a +, to indicate it's superior to n
+Any following ascii chars after ~ or + are ignored
+
+Examples:
+  1 < 2
+  2 > 2~dev
+  2 < 2+dev
+  2~dev < 2+dev
+
+
+IMAGES VERSIONNING
+__________________
+A valid version is an integer. Nothing more!
\ No newline at end of file
diff --git a/installsystems/image.py b/installsystems/image.py
index f9859ff50efcb77e2a87250e41b7a12c209962bd..f60053ad37b15f7e289ea88eb7c89d51826f53ae 100644
--- a/installsystems/image.py
+++ b/installsystems/image.py
@@ -51,34 +51,14 @@ class Image(object):
         if re.match("^\d+$", buf) is None:
             raise Exception("Invalid image version %s" % buf)
 
+
     @staticmethod
     def compare_versions(v1, v2):
         '''
-        Compare v1 and v2
-        return > 0 if v1 > v2
-        return < 0 if v2 > v1
-        return = 0 if v1 == v2
+        For backward compatibility, image class offer a method to compare image versions
+        But code is now inside tools
         '''
-        # check v1
-        try:
-            i1 = int(v1)
-        except ValueError:
-            if isinstance(v1, basestring):
-                v1m = re.search("\d+", v1)
-                if v1m is None:
-                    raise Exception("Invalid version %s" % v1)
-                i1 = int(v1m.group(0))
-        # check v2
-        try:
-            i2 = int(v2)
-        except ValueError:
-            if isinstance(v2, basestring):
-                v2m = re.search("\d+", v1)
-                if v2m is None:
-                    raise Exception("Invalid version %s" % v2)
-                i2 = int(v2m.group(0))
-        return i1 - i2
-
+        return istools.compare_versions(v1, v2)
 
 class SourceImage(Image):
     '''
diff --git a/installsystems/tools.py b/installsystems/tools.py
index 4a978952e1b0ddb61e80880e1daa012ec45c4558..2269f97f5ac1ade06588b33d8761c387187be4cc 100644
--- a/installsystems/tools.py
+++ b/installsystems/tools.py
@@ -463,3 +463,33 @@ def chroot(path, shell="/bin/bash", mount=True):
     call(["chroot", path, shell], close_fds=True)
     # revert preparation of chroot
     unprepare_chroot(path, mount)
+
+def compare_versions(v1, v2):
+    '''
+    This function compare version :param v1: and version :param v2:
+    Compare v1 and v2
+    return > 0 if v1 > v2
+    return < 0 if v2 > v1
+    return = 0 if v1 == v2
+    '''
+
+    def get_ver(version):
+        '''Return float version'''
+        if type(version) is int or type(version) is float:
+            return float(version)
+        elif isinstance(version, basestring):
+            iv = re.match("^(\d+)(?:([-~+])\w*)?$", version)
+            if iv is None:
+                raise TypeError('Invalid version: %s' % version)
+            rv = float(iv.group(1))
+            if iv.group(2) == "~":
+                rv -= 0.1
+            else:
+                rv += 0.1
+            return rv
+        else:
+            raise TypeError('Invalid version: %s' % version)
+
+    fv1 = get_ver(v1)
+    fv2 = get_ver(v2)
+    return fv1 - fv2