diff --git a/CCDpanelsetup.py b/CCDpanelsetup.py
index 9cd3360..62a235d 100644
--- a/CCDpanelsetup.py
+++ b/CCDpanelsetup.py
@@ -228,6 +228,10 @@ class buildpanel(tk.Frame):
 
   def jfsAddOns(self,CCDplot):
         
+        def darkline():
+              if (self.jf.do_save_darkline(config.rxData16)==1):
+                self.jfsdark_check.config(state=tk.NORMAL)
+        
         self.jfstitel = tk.Label(self, text=' Photometer ')
         #self.jfstitel.config(font=("Courier",0))
         self.jfstitel.grid(row=10,column=4,columnspan=2)
@@ -235,6 +239,10 @@ class buildpanel(tk.Frame):
         self.jfs4cal.grid(row=11,column=4)
         self.jfs4nm_check = tk.Checkbutton(self,text="[nm] scale on/off",variable=self.jf.nm_checked,command=lambda CCDplot=CCDplot: self.updateplot(CCDplot))
         self.jfs4nm_check.grid(row=12,column=4)
+        self.jfs4cal = tk.Button(self,text='save Darkline',fg="blue", command= darkline)
+        self.jfs4cal.grid(row=13,column=4)
+        self.jfsdark_check = tk.Checkbutton(self,text="Darkline on/off",variable=self.jf.darkline_checked,state=tk.DISABLED,command=lambda CCDplot=CCDplot: self.updateplot(CCDplot))
+        self.jfsdark_check.grid(row=14,column=4)
   
   ### Callbacks for traces, buttons, etc ###
   def callback(self):
@@ -311,10 +319,14 @@ class buildpanel(tk.Frame):
   def updateplot(self, CCDplot):
     #This subtracts the ADC-pixel from ADC-dark
     if (config.datainvert==1): 
-        config.pltData16 = (config.rxData16[10]+config.rxData16[11])/2 - config.rxData16
+        if (self.jf.get_darkline_checked()==1):
+          config.pltData16 = self.jf.darkData16 - config.rxData16
+        else:
+          config.pltData16 = (config.rxData16[10]+config.rxData16[11])/2 - config.rxData16
         #This subtracts the average difference between even and odd pixels from the even pixels
         if (config.balanced==1):
             config.offset = (config.pltData16[18]+config.pltData16[20]+config.pltData16[22]+config.pltData16[24]-config.pltData16[19]-config.pltData16[21]-config.pltData16[23]-config.pltData16[24])/4
+            #print(config.offset)
             for i in range (1847):
                 config.pltData16[2*i] = config.pltData16[2*i] - config.offset 
     CCDplot.a.clear()
diff --git a/JFSphoto.py b/JFSphoto.py
index aaa9603..6ff92ae 100644
--- a/JFSphoto.py
+++ b/JFSphoto.py
@@ -25,7 +25,11 @@ class Jfsphoto (object):
         ########## nm scale checkButton default nm-scale is off
         self.nm_checked = tk.IntVar()
         self.nm_checked.set(0)
-
+        ########## darkline 
+        self.darkData16 = np.zeros(3694, np.float32)
+        self.darkline_checked = tk.IntVar()
+        self.darkline_checked.set(0)
+        
     def do_calibrate(self):
         win = tk.Toplevel()
         win.geometry("450x200+100+100")
@@ -71,6 +75,27 @@ class Jfsphoto (object):
         win.grab_set()
         win.wait_window()
 
+    def do_msg(self,txt):
+        self.mroot = tk.Tk()
+        self.mroot.minsize(100,50)
+        self.mroot.title(" Info ")
+        self.label = tk.Label(self.mroot, text=txt,bg="yellow",fg="blue")
+        self.label.pack()
+        self.button = tk.Button(self.mroot, text='OK', width=25, command=self.mroot.destroy)
+        self.button.pack()
+        self.mroot.mainloop()
+
+    def do_save_darkline(self,dark):
+        x = np.min(dark)
+        if (x < 3700):
+            self.do_msg(" This is not a Darkline ")
+            return 0
+        else :    
+            self.darkData16 = dark*1.0
+            return 1
+
+    def get_darkline_checked(self):
+        return self.darkline_checked.get()
 
     def checkit(self):
         self.nm = int(self.tnm.get())
diff --git a/config.py b/config.py
index bff3369..fc2e392 100644
--- a/config.py
+++ b/config.py
@@ -2,7 +2,7 @@ import numpy as np
 
 
 #serial definitions
-port = 'COM3' #'/dev/ttyACM0'
+port = 'COM7' #'/dev/ttyACM0'
 baudrate = 115200
 
 #Data as the program handles
@@ -17,7 +17,7 @@ stopsignal = 0
 #Data arrays for received bytes
 rxData8 = np.zeros(7388, np.uint8)
 rxData16 = np.zeros(3694, np.uint16)
-pltData16 = np.zeros(3694, np.uint16)
+pltData16 = np.zeros(3694, np.float32)
 
 #Arrays for data to transmit
 txsh = np.uint8([0,0,0,0])