diff --git a/spectrum.py b/spectrum.py
index 4503252..96936b1 100755
--- a/spectrum.py
+++ b/spectrum.py
@@ -561,7 +561,6 @@ bias = {
 }
 
 mean_bias = np.mean( [ bias[ 'top' ] , bias[ 'down' ] ] , axis = 0 )
-mean_bias = 0
 
 if verbose:
     print( 'bias substraction finished' )
@@ -569,7 +568,7 @@ if verbose:
 mean_data = np.mean( data[
     spectrum[ 'y' ][ 'min' ] : spectrum[ 'y' ][ 'max' ],
     spectrum[ 'x' ][ 'min' ] : spectrum[ 'x' ][ 'max' ]
-] , axis = 0 )
+] , axis = 0 ) - mean_bias
 
 if intensity != None:
     if verbose:
@@ -689,6 +688,7 @@ if intensity != None:
         true_intensity_value = ( intensity_stairs.shape[0] - np.polyval( index_polyval , intensity_value ) ) * step
 
         final_intensity[index] = np.exp( true_intensity_value )
+        if final_intensity[ index ] > np.exp( 2.2 ):
 
     if verbose:
         print( 'intensity calibration finished' )
@@ -701,6 +701,8 @@ if output == None:
 else:
     if verbose:
         print( 'storing result in ' + output )
+    plt.plot( final_intensity[ 1 : - 1 ] )
+    plt.show()
     main_hdu  = fits.PrimaryHDU( final_intensity[1:-1] ) # remove -1
     main_hdu.header[ 'CRVAL1'   ] = wavelengths[0]
     main_hdu.header[ 'CDELT1'   ] = wavelengths[1] - wavelengths[0]