diff --git a/csvfile.py b/csvfile.py
index cdae917..4bd7ef0 100755
--- a/csvfile.py
+++ b/csvfile.py
@@ -1,4 +1,5 @@
 import csv
+from copy import copy
 from pathlib import Path
 
 class CSVFile:
@@ -35,6 +36,7 @@ class CSVFile:
                 self.__fields.append(field)
         self.__data.append(row)
         self.__addBuffer.append(row)
+        self.length = len(self.__data)
 
     def getRow(self,rowIdx):
         return self.__data[rowIdx]
@@ -118,7 +120,10 @@ class CSVFile:
             return count > 0
         return False
     
-    def fill(self, v=0):
-        if len(self.__data) == 0:
-            return False
-        return { k:v for k in self.__data[0].keys() }
\ No newline at end of file
+    def fill(self, row, fillV=0, updateKVs=[]):
+        row = copy(row)
+        for k in row:
+            row[k] = fillV
+        for kv in updateKVs:
+            row.update(kv)
+        self.addRow(row)
\ No newline at end of file
diff --git a/disk-usage.py b/disk-usage.py
index 9c587b4..b54b7da 100755
--- a/disk-usage.py
+++ b/disk-usage.py
@@ -7,6 +7,7 @@ from drive import Drive
 from csvfile import CSVFile
 from pathlib import Path
 from utils import subtract, nextWeek, sumKV
+from datetime import timedelta
 
 SEARCH_PATH = "/mnt/"
 
@@ -27,9 +28,28 @@ class DiskUsage:
         row.pop("next_week")
         return row
 
+    @staticmethod
+    def __update_weekly_data(csvfile, updatedRow, previousNextWeek, nextWeek, 
+                             makeEmpty=False, duplicateEmpty=0, updateLast=False):
+        if csvfile.length < 1:
+            if makeEmpty:
+                csvfile.fill(updatedRow,updateKVs=[{ "time" : (nextWeek + timedelta(days=-7)).isoformat() }])
+            for i in range(0,duplicateEmpty):
+                csvfile.addRow(updatedRow)
+            csvfile.addRow(updatedRow)
+        elif previousNextWeek == nextWeek.isoformat():
+            csvfile.replaceByKV("time", nextWeek.isoformat(), updatedRow, backwards=True, start=-1)
+        else:
+            csvfile.addRow(updatedRow)
+            previousWeeklyRow = updatedRow.copy()
+            previousWeeklyRow.update({ "time" : previousNextWeek })
+            if updateLast:
+                csvfile.replaceByKV("time", previousNextWeek, previousWeeklyRow, backwards=True, start=-1)
+        csvfile.efficientWriteFile()
+
 
     def update(self):
-        nextWeek_ = nextWeek().isoformat()
+        nextWeek_ = nextWeek()
 
         sizeDaily = CSVFile(self.SIZE_FILE)
         currentlyUsed = Drive.getUsed(SEARCH_PATH)
@@ -41,16 +61,8 @@ class DiskUsage:
         sizeWeekly = CSVFile(self.WEEKLY_SIZE_FILE)
         sizeWeeklyRow = self.__daily2weeklyRow(currentlyUsed)
         previousNextWeek = sizeDaily.getRow(-2).get("next_week")
-        if sizeWeekly.length < 1:
-            sizeWeekly.addRow(sizeWeeklyRow)
-        elif previousNextWeek == nextWeek_:
-            sizeWeekly.replaceByKV("time", nextWeek_, sizeWeeklyRow, backwards=True, start=-1)
-        else:
-            sizeWeekly.addRow(sizeWeeklyRow)
-            previousWeeklyRow = sizeWeeklyRow.copy()
-            previousWeeklyRow.update({ "time" : previousNextWeek })
-            sizeWeekly.replaceByKV("time", previousNextWeek, previousWeeklyRow, backwards=True, start=-1)
-        sizeWeekly.efficientWriteFile()
+        self.__update_weekly_data(sizeWeekly, sizeWeeklyRow, previousNextWeek, nextWeek_,
+                                  duplicateEmpty=1, updateLast=True)
 
         delta = subtract(sizeDaily.getRow(-1),sizeDaily.getRow(-2))
         diffDaily = CSVFile(self.DIFF_FILE)
@@ -61,19 +73,10 @@ class DiskUsage:
         if sizeWeekly.length < 2:
             return 0 # Break for new files
         diffWeekly = CSVFile(self.WEEKLY_DIFF_FILE)
-        previousNextWeek = diffDaily.getRow(-2).get("next_week")
-        delta = subtract(sizeWeekly.getRow(-1), sizeWeekly.getRow(-2))
-        print(previousNextWeek == nextWeek_)
+        diffWeeklyRow = subtract(sizeWeekly.getRow(-1), sizeWeekly.getRow(-2))
         print(delta)
-        if previousNextWeek == nextWeek_:
-            diffWeekly.replaceByKV("time", previousNextWeek, delta, backwards=True, start=-1)
-        else:
-            delta.update({ "time" : previousNextWeek })
-            diffWeekly.replaceByKV("time", previousNextWeek, delta, backwards=True, start=-1)
-            empty = diffDaily.fill()
-            empty.update({"time" : nextWeek_})
-            diffWeekly.addRow(empty)
-        diffWeekly.efficientWriteFile()
+        self.__update_weekly_data(diffWeekly, diffWeeklyRow, previousNextWeek, nextWeek_,
+                                  makeEmpty=True)
 
 if __name__ == '__main__':
     DiskUsage("/home/peter/scripts/datalogging/disk-usage/testfiles").update()
\ No newline at end of file
diff --git a/viewer.py b/viewer.py
index 23ace1f..8e90e0d 100755
--- a/viewer.py
+++ b/viewer.py
@@ -79,7 +79,7 @@ set grid xtics;
 
 PLOT_DIFF = """
 set autoscale y
-set ylabel '{/Symbol D}Used [ISO definition]' textcolor 'white';
+set ylabel '{/Symbol D}Used [SI definition]' textcolor 'white';
 set format y '%+08.3s %cB';
 
 set y2label '{/Symbol D}Used (GB)' textcolor 'white';
@@ -90,7 +90,7 @@ set format y2 '%+08.3s %c';
 PLOT_0="""set title 'Used capacity of disks (last 28 days)' textcolor 'white';
 
 set format y '%.2s %cB';
-set ylabel 'Used [ISO definition]' textcolor 'white';
+set ylabel 'Used [SI definition]' textcolor 'white';
 set ytics 0.25*10**12;
 set mytics 2;
 
@@ -119,7 +119,7 @@ set offset graph 0, graph 0, graph 0.02, graph 0.02;
 PLOT_2="""
 set title 'Used capacity of disks (last 364 days)' textcolor 'white';
 
-set ylabel 'Used [ISO definition]' textcolor 'white';
+set ylabel 'Used [SI definition]' textcolor 'white';
 set format y '%.2s %cB';
 set ytics 0.25*10**12;
 set mytics 2;