Index: branches/pap/psModules/src/detrend/pmGainTweak.c
===================================================================
--- branches/pap/psModules/src/detrend/pmGainTweak.c	(revision 28485)
+++ branches/pap/psModules/src/detrend/pmGainTweak.c	(revision 28485)
@@ -0,0 +1,59 @@
+#include <stdio.h>
+#include <pslib.h>
+
+#include "pmFPA.h"
+
+#include "pmGainTweak.h"
+
+bool pmGainTweak(const pmCell *cell)
+{
+    PS_ASSERT_PTR_NON_NULL(cell, false);
+    pmChip *chip = cell->parent;
+    PS_ASSERT_PTR_NON_NULL(chip, false);
+
+    int numCells = chip->cells;         // Number of cells
+    psVector *gains = psVectorAlloc(numCells, PS_TYPE_F32); // Gain for each cell
+    psVector *mask = psVectorAlloc(numCells, PS_TYPE_VECTOR_MASK); // Mask for gains
+    psVectorInit(mask, 0);
+    int numGood = 0;                    // Number of good gains
+
+   for (int i = 0; i < numCells; i++) {
+        pmCell *otherCell = chip->cells->data[i]; // A different cell
+        if (otherCell == cell) {
+            mask->data.PS_TYPE_VECTOR_MASK_DATA[i] = 0xFF;
+            continue;
+        }
+        float gain = psMetadataLookupF32(NULL, otherCell->concepts, "CELL.GAIN"); // Gain for cell
+        gains->data.F32[i] = gain;
+        if (!isfinite(gains->data.F32[i])) {
+            mask->data.PS_TYPE_VECTOR_MASK_DATA[i] = 0xFF;
+        } else {
+            numGood++;
+        }
+   }
+
+   if (numGood == 0) {
+       psError(PM_ERR_DETREND, true, "No other cell gains available with which to tweak gain.");
+       psFree(gains);
+       psFree(mask);
+       return false;
+   }
+
+   psStats *stats = psStatsAlloc(PS_STAT_SAMPLE_MEDIAN); // Statistics
+   if (!psVectorStats(stats, gains, NULL, mask, 0xFF)) {
+       psError(psErrorCodeLast(), false, "Unable to determine target gain");
+       psFree(stats);
+       psFree(gains);
+       psFree(mask);
+       return false;
+   }
+   float target = stats->sampleMedian;  // Target gain
+   psFree(stats);
+   psFree(gains);
+   psFree(mask);
+
+   psMetadataItem *item = psMetadataLookup(cell->concepts, "CELL.GAIN");
+   item->data.F32 = target;
+
+   return true;
+}