diff --git a/Civi/Api4/Action/ContactCategory/GetFlows.php b/Civi/Api4/Action/ContactCategory/GetFlows.php
index bc3f5cd..d86445d 100644
--- a/Civi/Api4/Action/ContactCategory/GetFlows.php
+++ b/Civi/Api4/Action/ContactCategory/GetFlows.php
@@ -3,6 +3,7 @@ namespace Civi\Api4\Action\ContactCategory;
 
 use CRM_Contactcats_ExtensionUtil as E;
 use Civi;
+use Civi\Api4\ContactCategoryDefinition;
 use Civi\Api4\Generic\Result;
 use CRM_Core_DAO;
 use CRM_Core_Exception;
@@ -296,10 +297,16 @@ class GetFlows extends \Civi\Api4\Generic\AbstractAction {
       2 => [$endDateYmd, 'Int'],
     ])->fetchAll();
 
+    // It's possible to end up with NULLs at the startSide.
+    // These should be replaced with our default category.
+    $defaultCategoryId = ContactCategoryDefinition::get()
+      ->addWhere('search_type:name', '=', 'default')
+      ->execute()->first()['id'];
+
     // Don't use exchange array so as not to gazump non-array data(?)
     foreach ($data as $row) {
       $result[] = [
-        'from_category_id' => (int) $row['from_category_id'],
+        'from_category_id' => (int) (($row['from_category_id']) ?: $defaultCategoryId),
         'to_category_id' => (int) $row['to_category_id'],
         'contact_count' => (int) $row['contact_count'],
       ];
@@ -313,8 +320,8 @@ class GetFlows extends \Civi\Api4\Generic\AbstractAction {
     try {
       $data = CRM_Core_DAO::executeQuery($sql, $params)->fetchAll();
     }
-    catch (\Exception $e) {
-      print $e->getCause()->userinfo;
+    catch (\CRM_Core_Exception $e) {
+      if (method_exists('getClause', $e)) print $e->getCause()->userinfo;
     }
     print "\n$msg (" . count($data) . ") records ===============================\n";
     foreach ($data as $row) {
diff --git a/ang/crmContactcats.js b/ang/crmContactcats.js
index f1a534b..9fb8e4a 100644
--- a/ang/crmContactcats.js
+++ b/ang/crmContactcats.js
@@ -47,6 +47,7 @@
         }
         // Ensure we have the minimum of what we need.
         if (!catDefs.find(c => c.search_type === 'default')) {
+          console.log("Adding default category as was missing");
           // There's no default one.
           catDefs.push(Object.assign({}, blankDefn, {
             execution_order: catDefs.length,
@@ -67,8 +68,11 @@
           ctrl[orderField] = catDefs.slice();
           ctrl[orderField].sort((a, b) => {
             // console.log({orderField, aST: a.search_type, bST: b.search_type, aOrd:a[orderField], bOrd:b[orderField], aLab:a.label, bLab:b.label});
-            if (a.search_type === 'default' && b.search_type !== 'default') return 1;
-            if (b.search_type === 'default' && a.search_type !== 'default') return -1;
+            if (orderField === 'execution_order') {
+              // Enforce default at end for assignment order
+              if (a.search_type === 'default' && b.search_type !== 'default') return 1;
+              if (b.search_type === 'default' && a.search_type !== 'default') return -1;
+            }
             if (a[orderField] > b[orderField]) return 1;
             if (a[orderField] < b[orderField]) return -1;
             if (a.label < b.label) return 1;
@@ -162,6 +166,16 @@
           ctrl.view = 'list';
         }
 
+        ctrl.canMoveBelow = function(row, idx) {
+          // Only show move buttons when moving.
+          if (ctrl.moveIdx === null) return false;
+
+          if (ctrl.uxOrderField === 'execution_order') {
+            // The default MUST be the last item in execution_order.
+            if (row.search_type === 'default') return false;
+          }
+          return (idx + 1 < ctrl.moveIdx || idx > ctrl.moveIdx);
+        };
         /**
          * Move a category within the currently selected order.
          */
diff --git a/ang/crmContactcats/crmContactCategoryFlows.html b/ang/crmContactcats/crmContactCategoryFlows.html
index da07896..8c19be2 100644
--- a/ang/crmContactcats/crmContactCategoryFlows.html
+++ b/ang/crmContactcats/crmContactCategoryFlows.html
@@ -2,20 +2,29 @@
   <form crm-ui-id-scope >
     <div crm-ui-field="{name: 'cc.startDate', title: ts('Start date')}" >
       <input
-          crm-ui-id="ci.startDate"
+          crm-ui-id="cc.startDate"
           type=date
-          name="startDate"
+          name=startDate
           ng-model="$ctrl.startDate"
           />
     </div>
     <div crm-ui-field="{name: 'cc.endDate', title: ts('End date')}" >
       <input
-          crm-ui-id="ci.endDate"
+          crm-ui-id="cc.endDate"
           type=date
-          name="endDate"
+          name=endDate
           ng-model="$ctrl.endDate"
           />
     </div>
+    <div crm-ui-field="{name: 'cc.changesOnly', title: ts('Show changes only')}" >
+      <input
+          crm-ui-id="cc.changesOnly"
+          type=checkbox
+          name=changesOnly
+          ng-model="$ctrl.changesOnly"
+          ng-change="$ctrl.redrawSankey()"
+          />
+    </div>
     <div>
       <button ng-click="$ctrl.fetchStats()"  >
         <i ng-if="$ctrl.loading" class="crm-i fa-spin fa-spinner"></i>
@@ -47,7 +56,7 @@
                 fill="{{p.fill}}"
                 fill-opacity=0.5
                 >
-                <title>{{p.source.contact_count}} {{p.fromCat.name}} → {{p.toCat.name}}</title>
+                <title>{{p.source.contact_count}} {{p.fromCat.label}} → {{p.toCat.label}}</title>
           </path>
           <!--
           <g ng-repeat="label in $ctrl.sankey.labels">
diff --git a/ang/crmContactcats/crmContactCategoryFlows.js b/ang/crmContactcats/crmContactCategoryFlows.js
index 3eae11c..4e5d26c 100644
--- a/ang/crmContactcats/crmContactCategoryFlows.js
+++ b/ang/crmContactcats/crmContactCategoryFlows.js
@@ -10,10 +10,120 @@
       // Development: set this true to use a small defined fixture instead of real data.
       const useTestFixtures = false;
 
+      let allFlowsData;
+
+      ctrl.redrawSankey = function() {
+        let flowsData = ctrl.changesOnly
+          ? allFlowsData.filter(({from_category_id, to_category_id}) => from_category_id != to_category_id)
+          : allFlowsData;
+
+        // Process the results into something useful.
+        ctrl.loading = false;
+        const labelWidth = ctrl.sankey.labelWidth,
+          width = Math.max(600, document.querySelector('.contact-cats-sankey').clientWidth),
+          snakeWidth = width - 2*labelWidth;
+        ctrl.sankey.width = width;
+
+        if (!(flowsData.length)) {
+          ctrl.noStats = true;
+          ctrl.stats = [];
+          return;
+        }
+        ctrl.noStats = false;
+
+        // Create main analysis structure, indexed by right hand side of snakes.
+        const analysis = {}, offsetWithinSourcesByCat = {};
+        ctrl.catDefs.forEach(cat => {
+          analysis[cat.id] = { sources: [], now: 0, previous: 0, cat };
+          offsetWithinSourcesByCat[cat.id] = 0;
+        });
+
+        let totalContacts = 0;
+        flowsData.forEach(row => {
+          const {from_category_id, to_category_id, contact_count} = row;
+          if (!from_category_id) {
+            // from nowhere: ignore for now.
+            console.log("Skipping", row);
+            return; 
+          }
+          analysis[to_category_id].now += contact_count;
+          if (!catDefsIndexed[from_category_id]) {
+            console.log("from_category_id", from_category_id,  "not found in defs", catDefsIndexed);
+          }
+          analysis[from_category_id].previous += contact_count;
+          analysis[to_category_id].sources.push({ cat: catDefsIndexed[from_category_id], contact_count });
+
+          totalContacts += contact_count;
+        });
+
+        // allowing 50px per cat
+        let scale = (ctrl.sankey.height - (ctrl.catDefs.length * 8)) / totalContacts;
+
+        let previousCatHeight = 0;
+        ctrl.catDefs.forEach(cat => {
+          // Now we know how many contacts per category per side.
+          // Set the from offsets
+          offsetWithinSourcesByCat[cat.id] = previousCatHeight;
+          previousCatHeight += analysis[cat.id].previous * scale +8; // padding TODO: standardise
+
+          // Make sure that our 'from' snake ends are ordered by category presentation_order
+          // This avoids one categories snakes overlapping its others.
+          analysis[cat.id].sources.sort((a, b) => {
+            return a.cat.presentation_order - b.cat.presentation_order;
+          })
+        });
+
+        // Make a list of snakes we need to draw.
+        const snakes = [];
+        let yTopR = 0;
+        ctrl.catDefs.forEach(cat => {
+          let toCat = analysis[cat.id];
+          toCat.yTop = yTopR;
+          toCat.sources.forEach(source => {
+            const sourceHeight = parseInt(source.contact_count * scale);
+            const gradientId = 'contactcats-gradient-' + source.cat.id + '-' + cat.id;
+            snakes.push({
+              source,
+              gradientId,
+              toTop : yTopR,
+              toHeight : Math.max(1,sourceHeight),
+              toCat: toCat.cat,
+              fromTop: offsetWithinSourcesByCat[source.cat.id],
+              fromHeight: Math.max(1,sourceHeight), // from and to heights will be the same!
+              fromCat: source.cat
+            });
+            offsetWithinSourcesByCat[source.cat.id] += sourceHeight;
+            yTopR += sourceHeight;
+          });
+          yTopR += 8;// padding TODO: apply this to the lhs too
+        });
+
+
+
+        // Create the SVG data for the snakes.
+        //c${-snakeWidth/4},0,${-snakeWidth},${-snakeWidth*3/4},0,${-snakeWidth}, ${snake.fromTopOffset + snake.fromHeight - snake.toTop - snake.toHeight}
+        const curve1 = snakeWidth/4, curve2 = snakeWidth*3/4;
+        snakes.forEach(snake => {
+          const dyBottom = snake.fromTop + snake.fromHeight - snake.toTop - snake.toHeight;
+          const dyTop = -snake.fromTop + snake.toTop;
+          snake.d = `M${snakeWidth},${snake.toTop} l0,${snake.toHeight}
+                c${-curve1},0,${-curve2},${dyBottom},${-snakeWidth},${dyBottom}
+                l0,${-snake.fromHeight}
+                c${curve1},0,${curve2},${dyTop},${snakeWidth},${dyTop}
+                z
+              `;
+          snake.fill = `url(#${snake.gradientId})`;
+        });
+
+        ctrl.sankey.snakes = snakes;
+        console.log({snakes, catDefs: catDefsIndexed, analysis});
+      }
+
       // this.$onInit gets run after the this controller is called, and after the bindings have been applied.
       this.$onInit = async function() {
         // Default start date to 1 month ago.
         ctrl.loading = true;
+        ctrl.changesOnly = false;
         ctrl.startDate = new Date();
         ctrl.startDate.setMonth(ctrl.startDate.getMonth() - 1);
         ctrl.startDate.setHours(0);
@@ -22,14 +132,15 @@
         if (useTestFixtures) {
           ctrl.startDate = new Date('2025-03-10');
         }
+        ctrl.startDate = new Date('2025-03-10');
         ctrl.endDate = null;
         ctrl.stats = null;
         ctrl.sankey = { height: 500, width: 900, labelWidth: 150, snakeWidth: 600, snakes: [] };
 
         if (useTestFixtures) {
           ctrl.catDefs = [
-            { id: 100, name: 'Amazing', color:'#4ad926' },
-            { id: 101, name: 'Meh', color:'#d52a80' },
+            { id: 100, label: 'Amazing', color:'#ffcc00' },
+            { id: 101, label: 'Meh', color:'#ff6f00' },
           ];
         }
         else {
@@ -37,9 +148,9 @@
             crmApi4("ContactCategoryDefinition", 'get', { orderBy: { presentation_order: 'ASC' }, withLabels: true })
           );
         }
+        ctrl.sankey.height = ctrl.catDefs.length * 50;
         ctrl.loading = false;
         ctrl.catDefs.forEach(cat => {catDefsIndexed[cat.id] = cat;});
-        console.log(catDefsIndexed);
 
         ctrl.fetchStats = function() {
           ctrl.loading = true;
@@ -59,110 +170,8 @@
             })
           }
           chain.then(r => {
-            // Process the results into something useful.
-            ctrl.loading = false;
-            const labelWidth = ctrl.sankey.labelWidth,
-              width = Math.max(600, document.querySelector('.contact-cats-sankey').clientWidth),
-              snakeWidth = width - 2*labelWidth;
-            ctrl.sankey.width = width;
-
-            if (!(r.length)) {
-              ctrl.noStats = true;
-              ctrl.stats = [];
-              return;
-            }
-            ctrl.noStats = false;
-
-            // Create main analysis structure, indexed by right hand side of snakes.
-            const analysis = {}, offsetWithinSourcesByCat = {};
-            ctrl.catDefs.forEach(cat => {
-              analysis[cat.id] = { sources: [], now: 0, previous: 0, cat };
-              offsetWithinSourcesByCat[cat.id] = 0;
-            });
-
-            let totalContacts = 0;
-            r.forEach(row => {
-              const {from_category_id, to_category_id, contact_count} = row;
-              if (!from_category_id) {
-                // from nowhere: ignore for now.
-                console.log("Skipping", row);
-                return; 
-              }
-              analysis[to_category_id].now += contact_count;
-              if (!catDefsIndexed[from_category_id]) {
-                console.log("from_category_id", from_category_id,  "not found in defs", catDefsIndexed);
-              }
-              analysis[from_category_id].previous += contact_count;
-              analysis[to_category_id].sources.push({ cat: catDefsIndexed[from_category_id], contact_count });
-
-              totalContacts += analysis[to_category_id].now;
-            });
-
-
-            // allowing 50px per cat
-            let scale = (ctrl.catDefs.length * 50) / totalContacts;
-
-            let previousCatHeight = 0;
-            ctrl.catDefs.forEach(cat => {
-              // Now we know how many contacts per category per side.
-              // Set the from offsets
-              offsetWithinSourcesByCat[cat.id] = previousCatHeight;
-              previousCatHeight += Math.max(1, parseInt(analysis[cat.id].previous * scale)) +8; // padding TODO: standardise
-
-              // Make sure that our 'from' snake ends are ordered by category presentation_order
-              // This avoids one categories snakes overlapping its others.
-              analysis[cat.id].sources.sort((a, b) => {
-                if (!b.cat) {
-                  console.log("Sort fail on b", {a, b});
-                }
-                return a.cat.presentation_order - b.cat.presentation_order;
-              })
-            });
-
-            // Make a list of snakes we need to draw.
-            const snakes = [];
-            let yTopR = 0;
-            ctrl.catDefs.forEach(cat => {
-              let toCat = analysis[cat.id];
-              toCat.yTop = yTopR;
-              toCat.sources.forEach(source => {
-                const sourceHeight = Math.max(1,parseInt(source.contact_count * scale));
-                const gradientId = 'contactcats-gradient-' + source.cat.id + '-' + cat.id;
-                snakes.push({
-                  source,
-                  gradientId,
-                  toTop : yTopR,
-                  toHeight : sourceHeight,
-                  toCat: toCat.cat,
-                  fromTop: offsetWithinSourcesByCat[source.cat.id],
-                  fromHeight: sourceHeight, // from and to heights will be the same!
-                  fromCat: source.cat
-                });
-                offsetWithinSourcesByCat[source.cat.id] += sourceHeight;
-                yTopR += sourceHeight;
-              });
-              yTopR += 8;// padding TODO: apply this to the lhs too
-            });
-
-
-
-            // Create the SVG data for the snakes.
-                //c${-snakeWidth/4},0,${-snakeWidth},${-snakeWidth*3/4},0,${-snakeWidth}, ${snake.fromTopOffset + snake.fromHeight - snake.toTop - snake.toHeight}
-            const curve1 = snakeWidth/4, curve2 = snakeWidth*3/4;
-            snakes.forEach(snake => {
-              const dyBottom = snake.fromTop + snake.fromHeight - snake.toTop - snake.toHeight;
-              const dyTop = -snake.fromTop + snake.toTop;
-              snake.d = `M${snakeWidth},${snake.toTop} l0,${snake.toHeight}
-                c${-curve1},0,${-curve2},${dyBottom},${-snakeWidth},${dyBottom}
-                l0,${-snake.fromHeight}
-                c${curve1},0,${curve2},${dyTop},${snakeWidth},${dyTop}
-                z
-              `;
-              snake.fill = `url(#${snake.gradientId})`;
-            });
-
-            ctrl.sankey.snakes = snakes;
-            console.log({snakes, catDefs: catDefsIndexed, analysis});
+            allFlowsData = r;
+            ctrl.redrawSankey();
           });
         }
         // do initial fetch.
diff --git a/ang/crmContactcats/crmContactCategorySettings.html b/ang/crmContactcats/crmContactCategorySettings.html
index 2a678da..b699d6b 100644
--- a/ang/crmContactcats/crmContactCategorySettings.html
+++ b/ang/crmContactcats/crmContactCategorySettings.html
@@ -66,7 +66,7 @@
               <button ng-if="$ctrl.moveIdx === null && row.deleted" ng-click="row.deleted = false;$ctrl.dirty = 'dirty';">
                 <i class="fa-trash crm-i"></i> {{ts('Un-Delete')}}
               </button>
-              <button ng-if="$ctrl.moveIdx === null && !row.deleted && row.search_type !== 'default'" ng-click="$ctrl.moveIdx = idx" 
+              <button ng-if="$ctrl.moveIdx === null && !row.deleted && !(row.search_type === 'default' && $ctrl.uxOrderField === 'execution_order')" ng-click="$ctrl.moveIdx = idx" 
                      class="btn"
                       ng-disabled="$ctrl.presentation_order.length === 1"
                 >
@@ -78,7 +78,8 @@
                 <i class="fa-circle-xmark crm-i"></i> {{ts('Cancel Move')}}
               </button>
               <button ng-click="$ctrl.moveTo(idx)" ng-show="$ctrl.moveIdx !== null && (idx === 0 && $ctrl.moveIdx > 0)" ><i class="fa-sort-up crm-i" ></i>{{ts('Before this')}}</button>
-              <button ng-click="$ctrl.moveTo(idx+1)" ng-show="$ctrl.moveIdx !== null && row.search_type !== 'default' && (idx + 1 < $ctrl.moveIdx || idx > $ctrl.moveIdx)"><i class="fa-sort-down crm-i" ></i>{{ts('After this')}}</button>
+              <button ng-click="$ctrl.moveTo(idx+1)" ng-show="$ctrl.canMoveBelow(row, idx)"
+                ><i class="fa-sort-down crm-i" ></i>{{ts('After this')}}</button>
             </span>
           </div>
         </div>
@@ -156,11 +157,13 @@
             name="search_type"
             ng-model="$ctrl.categoryToEdit.search_type"
             ng-change="$ctrl.fixSearchData()"
+            ng-show="$ctrl.categoryToEdit.search_type !== 'default'"
             >
             <option value="search" >{{ts('Search Kit search')}}</option>
             <option value="group" >{{ts('Group')}}</option>
             <!-- future? <option value="sql_template" >{{ts('SQL template')}}</option> -->
         </select>
+        <div ng-show="$ctrl.categoryToEdit.search_type === 'default'" >{{ts('Default category')}}</div>
       </div>
 
       <!-- fields for search kit -->