diff --git a/site-modules/profile/files/stats_exporter/export-archive_counters.py b/site-modules/profile/files/stats_exporter/export-archive_counters.py
index f1615c98..e1ada205 100755
--- a/site-modules/profile/files/stats_exporter/export-archive_counters.py
+++ b/site-modules/profile/files/stats_exporter/export-archive_counters.py
@@ -1,51 +1,89 @@
 #!/usr/bin/python3
 
 import requests
 import json
 import time
 
-def clean_item(item):
+
+def adapt_format(item):
     """Javascript expects timestamps to be in milliseconds
        and counter values as floats
 
+    Args
+        item (list): List of 2 elements, timestamp and counter
+
+    Return:
+        Normalized tuple (timestamp in js expected time, counter as float)
+
     """
     timestamp = int(item[0])
     counter_value = item[1]
     return [timestamp*1000, float(counter_value)]
-    
 
-def get_timestamp_history(label):
-    result = []
-    rrd_data = []
+
+def compute_url(label, server='pergamon.internal.softwareheritage.org', port=9090):
+    """Compute the api url to request data from, specific to a label.
+
+    """
     now = int(time.time())
-    url = 'http://pergamon.internal.softwareheritage.org:9090/api/v1/query_range?'
-    url = url + 'query=sum(sql_swh_archive_object_count{object_type="%s"})' % label
-    url = url + '&start=1544543227&end=%s&step=12h' % now
+    url = 'http://%s:%s/api/v1/query_range?query=sum(sql_swh_archive_object_count{object_type="%s"})&start=1544543227&end=%s&step=12h' % (server, port, label, now)  # noqa
+    return url
+
 
-    # We only want to process timevalues for Source files
-    if (label == "content"):
-        # Historical data has already been processed for javascript usage
-        # No need to clean it further
-        with open("/usr/local/share/swh-data/history-counters.munin.json", "r") as f:
-            rrd_data = json.load(f)[label]
+def history_data(history_data_file="/usr/local/share/swh-data/history-counters.munin.json"):
+    """Retrieve the history from the history_data_file
 
+    Args:
+        history_data_file (str): Path to history file to load from
+
+    Returns:
+        dict with key (label in origin, revision, content), values (list of
+        history points: timestamp, counter):
+
+    """
+    with open(history_data_file, "r") as f:
+        return json.load(f)
+
+
+def get_timestamp_history(label):
+    """Given a label, retrieve its associated graph data.
+
+    Args:
+        label (str): Label object in {content, origin, revision}
+    """
+    result = []
+    url = compute_url(label)
     response = requests.get(url)
     if response.ok:
         data = response.json()
-        # In contrast, Prometheus-provided data has to be adapted to
-        # Javascript expectations
-        result = [clean_item(i) for i in
+        # data answer format:
+        # {"status":"success","data":{"result":[{"values":[[1544586427,"5375557897"]...  # noqa
+        # Prometheus-provided data has to be adapted to js expectations
+        result = [adapt_format(i) for i in
             data['data']['result'][0]['values']]
-    return rrd_data + result
+    return result
 
 
 def main():
-   result = {}
-   for label in ['content', 'origin', 'revision']:
-       result[label] = get_timestamp_history(label)
-   return result
-    
+    """Compute the history graph data for the label/object_type {content,
+    revision, origin}.
+
+    This retrieves data from prometheus' sql exporter (and adapt them to the
+    expected format of the flot library we use).
+
+    For content, that also retrieves old data fetched from a previous data file
+    and aggregates it to the new prometheus data.
+
+    """
+    result = {}
+    hist_data = history_data()
+    # for content, we retrieve existing data and merges with the new one
+    result['content'] = hist_data['content'] + get_timestamp_history('content')
+    for label in ['origin', 'revision']:
+        result[label] = get_timestamp_history(label)
+    return result
+
 
 if __name__ == '__main__':
     r = main()
     print(json.dumps(r))