Index: /fact/tools/pyscripts/pyfact/extractor.py
===================================================================
--- /fact/tools/pyscripts/pyfact/extractor.py	(revision 12950)
+++ /fact/tools/pyscripts/pyfact/extractor.py	(revision 12951)
@@ -82,5 +82,8 @@
                         continue
                 if ( pix_data[i] * pix_data[i+1] <= 0 ):
-                    time = (pix_data[i+1]*i-pix_data[i]*(i+1))
+                    # interpolate time of zero crossing with 
+                    # linear polynomial: y = ax + b
+                    a = (pix_data[i+1] - pix_data[i]) / ((i+1) - i)
+                    time = -1.0/a * pix_data[i] + i
                     hits.append(time)
             all_hits.append(hits)