diff --git a/kaart.py b/kaart.py
index ecb6d608952aa8827c71944e14b630c541b5154f..95de0001fa2625cc67a6d33584595968718f88ab 100755
--- a/kaart.py
+++ b/kaart.py
@@ -56,11 +56,13 @@ s.start()
 dt = Telescope(consoleHost='localhost')
 
 data = np.zeros((360, 720), dtype=float)
+data[:, :] = np.nan
 npoints = np.zeros(data.shape, dtype='i8')
 
 # create plot
 plt.ion()
 fig, ax = plt.subplots()
+fig.canvas.manager.set_window_title(f'Scan met de Dwingeloo telescoop {Time.now().iso[:16]}')
 fig.canvas.mpl_connect('close_event', set_stoprequest)
 
 plot = ax.imshow(data, origin='lower', extent=(-180.25, 179.75, -90.25, 89.75))
@@ -113,6 +115,8 @@ while not stoprequest:
     b = lat_to_pixel(pos.b.deg)
 
     n = npoints[b, l]
+    if np.isnan(data[b, l]):
+        data[b, l] = 0
     data[b, l] = (signal + n * data[b, l]) / (n + 1)
     npoints[b, l] += 1