diff --git a/README.md b/README.md
index da95988c20f01645139cbbf79b95c15117a4055b..335a35c274cab7079a5b5b5c9b9ffb2ba33e124a 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@
 version-checker
 ===============
 
-Tool for checking if software versions are out of date. Supports (for now) checking against github releases, dockerhub images, debian packages and arbitrary web sites (using regexp). Will start a webserver that exposes the version status as prometheus metyrics under the path '/metrics' and show a status page for all other paths.
+Tool for checking if software versions are out of date. Supports (for now) checking against github releases, dockerhub images, debian packages and arbitrary web sites (using regexp). Will start a webserver that exposes the version status as prometheus metrics under the path '/metrics' and show a status page for all other paths.
 
 Installation:
 -------------
@@ -65,3 +65,16 @@ Further keys depend on the check used:
 * website
   * url: url of the website
   * pattern: regex pattern for the version string, must contain exactly one capture group (for the version)
+
+Metrics
+-------
+
+Prometheus compatible metrics are available at the path /metrics. The series have the name `fhg_iam_version`. They have three labels:
+* `name` - corresponds to `name` in the config
+* `latest` - latest version available (according the the pattern)
+* `running` - this is `version` given in the config
+
+There are three possible values:
+* 0 - up to date, i.e. latest and running are identical
+* 1 - out of date, i.e. latest and running differ
+* 2 - unknown, the `latest` version could not be determined; latest will be `None` in this case
diff --git a/vcheck.py b/vcheck.py
index d0680b3874666ac56641aa7d7d7d01278655abbd..a1aa328d91831c0086ac9ce9e20fa1210e30e88d 100755
--- a/vcheck.py
+++ b/vcheck.py
@@ -267,9 +267,10 @@ def check(confd, v):
 
         if not current:
             res += td(c['name'], c['version'], f'UNKNOWN: {error}', 'unknown')
+            v.labels(name=c['name'], running=c['version'], latest=current).set(2)
             err += 1
         else:
-            uptodate = c['version'] == current
+            uptodate = not c['version'] == current
             res += td(c['name'], c['version'], current, 'uptodate' if uptodate else 'outofdate')
             v.labels(name=c['name'], running=c['version'], latest=current).set(uptodate)
             ood += not uptodate
@@ -319,7 +320,7 @@ def params():
 
 
 def run(port, confd, recheck):
-    v = prometheus_client.Gauge('version', 'Software version, value: 1 if up to date', ['name', 'running', 'latest'])
+    v = prometheus_client.Gauge('fhg_iam_version', 'Software version, value: 0 if up to date, 2 unknown', ['name', 'running', 'latest'])
 
     global content
     global running