Index: trunk/psModules/src/detrend/pmDark.h
===================================================================
--- trunk/psModules/src/detrend/pmDark.h	(revision 18163)
+++ trunk/psModules/src/detrend/pmDark.h	(revision 18859)
@@ -25,9 +25,14 @@
 
 
-// Combine darks
+// Combine darks -- preparation step
+bool pmDarkCombinePrepare(pmCell *output,      // Output cell; readouts will be attached
+			  const psArray *inputs, // Input readouts for combination
+			  psArray *ordinates,  // Ordinates for fitting
+			  const char *normConcept // Concept name to use to divide input pixel values
+    );
+
+// Combine darks -- do the actual work
 bool pmDarkCombine(pmCell *output,      // Output cell; readouts will be attached
                    const psArray *inputs, // Input readouts for combination
-                   psArray *ordinates,  // Ordinates for fitting
-                   const char *normConcept, // Concept name to use to divide input pixel values
                    int iter,            // Number of rejection iterations
                    float rej,           // Rejection threshold (standard deviations)