diff --git a/PWGCF/Flow/Tasks/flowTask.cxx b/PWGCF/Flow/Tasks/flowTask.cxx
index 447ceeaa5d6..ec583bdabd8 100644
--- a/PWGCF/Flow/Tasks/flowTask.cxx
+++ b/PWGCF/Flow/Tasks/flowTask.cxx
@@ -243,6 +243,7 @@ struct FlowTask {
     std::vector<float> nPt; // fraction of particles in each pT bin in one event
     std::vector<std::shared_ptr<TProfile2D>> listNptV2;
     std::vector<std::shared_ptr<TH2>> listPtX;
+    O2_DEFINE_CONFIGURABLE(cfgManualCk, bool, false, "Produce pt-pt variance")
   } cfgAdditionObs;
 
   ConfigurableAxis axisPt{"axisPt", {VARIABLE_WIDTH, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.5, 4, 5, 6, 8, 10}, "pt axis for histograms"};
@@ -287,7 +288,7 @@ struct FlowTask {
   std::vector<GFW::CorrConfig> corrconfigs;
   GFWCorrConfigs gfwConfigs;
   std::vector<GFW::CorrConfig> corrconfigsPtVn;
-  TAxis* fPtAxis;
+  TAxis* fPtAxis = nullptr;
   TRandom3* fRndm = new TRandom3(0);
   std::vector<std::pair<double, double>> etagapsPtPt;
   std::vector<std::vector<std::shared_ptr<TProfile>>> bootstrapArray;
@@ -324,15 +325,15 @@ struct FlowTask {
   double mMinSeconds{-1.};
   std::unordered_map<int, TH2*> gHadronicRate;
   ctpRateFetcher mRateFetcher;
-  TH2* gCurrentHadronicRate;
+  TH2* gCurrentHadronicRate = nullptr;
   RCTFlagsChecker rctChecker{"CBT"};
 
   // phi-EP correction
   std::vector<TF1*> funcEff;
-  TH1D* hFindPtBin;
-  TF1* funcV2;
-  TF1* funcV3;
-  TF1* funcV4;
+  TH1D* hFindPtBin = nullptr;
+  TF1* funcV2 = nullptr;
+  TF1* funcV3 = nullptr;
+  TF1* funcV4 = nullptr;
 
   void init(InitContext const&)
   {
@@ -439,6 +440,13 @@ struct FlowTask {
       registry.add("hPtA_afterDptCut", "p_{T} distribution", {HistType::kTH1D, {axisPt}});
       registry.add("hPtB_afterDptCut", "p_{T} distribution", {HistType::kTH1D, {axisPt}});
     }
+    if (cfgAdditionObs.cfgManualCk) {
+      registry.add("ptpt_1sub1_1sub3_2pc", "", {HistType::kTProfile, {axisIndependent}});
+      registry.add("pt_1sub1_1pc", "", {HistType::kTProfile, {axisIndependent}});
+      registry.add("pt_1sub1_2pc", "", {HistType::kTProfile, {axisIndependent}});
+      registry.add("pt_1sub3_1pc", "", {HistType::kTProfile, {axisIndependent}});
+      registry.add("pt_1sub3_2pc", "", {HistType::kTProfile, {axisIndependent}});
+    }
     if (doprocessMCGen) {
       registry.add("MCGen/MChPhi", "#phi distribution", {HistType::kTH1D, {axisPhi}});
       registry.add("MCGen/MChEta", "#eta distribution", {HistType::kTH1D, {axisEta}});
@@ -910,30 +918,30 @@ struct FlowTask {
     if (cfgUserIO.cfgAcceptance.value.empty() == false) {
       mAcceptance = ccdb->getForTimeStamp<GFWWeights>(cfgUserIO.cfgAcceptance, timestamp);
       if (mAcceptance)
-        LOGF(info, "Loaded acceptance weights from %s (%p)", cfgUserIO.cfgAcceptance.value.c_str(), (void*)mAcceptance);
+        LOGF(info, "Loaded acceptance weights from %s (%p)", cfgUserIO.cfgAcceptance.value.c_str(), static_cast<void*>(mAcceptance));
       else
-        LOGF(warning, "Could not load acceptance weights from %s (%p)", cfgUserIO.cfgAcceptance.value.c_str(), (void*)mAcceptance);
+        LOGF(warning, "Could not load acceptance weights from %s (%p)", cfgUserIO.cfgAcceptance.value.c_str(), static_cast<void*>(mAcceptance));
     }
     if (cfgUserIO.cfgEfficiency.value.empty() == false) {
       mEfficiency = ccdb->getForTimeStamp<TH1D>(cfgUserIO.cfgEfficiency, timestamp);
       if (mEfficiency == nullptr) {
         LOGF(fatal, "Could not load efficiency histogram for trigger particles from %s", cfgUserIO.cfgEfficiency.value.c_str());
       }
-      LOGF(info, "Loaded efficiency histogram from %s (%p)", cfgUserIO.cfgEfficiency.value.c_str(), (void*)mEfficiency);
+      LOGF(info, "Loaded efficiency histogram from %s (%p)", cfgUserIO.cfgEfficiency.value.c_str(), static_cast<void*>(mEfficiency));
     }
     if (cfgUserIO.cfgEfficiencyForNch.value.empty() == false) {
       mEfficiencyForNch = ccdb->getForTimeStamp<TH1D>(cfgUserIO.cfgEfficiencyForNch, timestamp);
       if (mEfficiencyForNch == nullptr) {
         LOGF(fatal, "Could not load efficiency histogram for trigger particles from %s", cfgUserIO.cfgEfficiencyForNch.value.c_str());
       }
-      LOGF(info, "Loaded efficiency histogram from %s (%p)", cfgUserIO.cfgEfficiencyForNch.value.c_str(), (void*)mEfficiencyForNch);
+      LOGF(info, "Loaded efficiency histogram from %s (%p)", cfgUserIO.cfgEfficiencyForNch.value.c_str(), static_cast<void*>(mEfficiencyForNch));
     }
     if (cfgAdditionObs.cfgDptDisEnable && cfgAdditionObs.cfgDptDishEvAvgMeanPt.value.empty() == false) {
       cfgAdditionObs.hEvAvgMeanPt = ccdb->getForTimeStamp<TH1D>(cfgAdditionObs.cfgDptDishEvAvgMeanPt, timestamp);
       if (cfgAdditionObs.hEvAvgMeanPt == nullptr) {
         LOGF(fatal, "Could not load mean pT histogram from %s", cfgAdditionObs.cfgDptDishEvAvgMeanPt.value.c_str());
       }
-      LOGF(info, "Loaded mean pT histogram from %s (%p)", cfgAdditionObs.cfgDptDishEvAvgMeanPt.value.c_str(), (void*)cfgAdditionObs.hEvAvgMeanPt);
+      LOGF(info, "Loaded mean pT histogram from %s (%p)", cfgAdditionObs.cfgDptDishEvAvgMeanPt.value.c_str(), static_cast<void*>(cfgAdditionObs.hEvAvgMeanPt));
     }
     if (cfgAdditionObs.cfgDptDisEnable && cfgAdditionObs.cfgDptDisSelectionSwitch > kNoDptCut) {
       if (cfgAdditionObs.cfgDptDisCutLow.value.empty() == false) {
@@ -941,14 +949,14 @@ struct FlowTask {
         if (cfgAdditionObs.fDptDisCutLow == nullptr) {
           LOGF(fatal, "Could not load dptDis low cut histogram from %s", cfgAdditionObs.cfgDptDisCutLow.value.c_str());
         }
-        LOGF(info, "Loaded dptDis low cut histogram from %s (%p)", cfgAdditionObs.cfgDptDisCutLow.value.c_str(), (void*)cfgAdditionObs.fDptDisCutLow);
+        LOGF(info, "Loaded dptDis low cut histogram from %s (%p)", cfgAdditionObs.cfgDptDisCutLow.value.c_str(), static_cast<void*>(cfgAdditionObs.fDptDisCutLow));
       }
       if (cfgAdditionObs.cfgDptDisCutHigh.value.empty() == false) {
         cfgAdditionObs.fDptDisCutHigh = ccdb->getForTimeStamp<TH1D>(cfgAdditionObs.cfgDptDisCutHigh, timestamp);
         if (cfgAdditionObs.fDptDisCutHigh == nullptr) {
           LOGF(fatal, "Could not load dptDis high cut histogram from %s", cfgAdditionObs.cfgDptDisCutHigh.value.c_str());
         }
-        LOGF(info, "Loaded dptDis high cut histogram from %s (%p)", cfgAdditionObs.cfgDptDisCutHigh.value.c_str(), (void*)cfgAdditionObs.fDptDisCutHigh);
+        LOGF(info, "Loaded dptDis high cut histogram from %s (%p)", cfgAdditionObs.cfgDptDisCutHigh.value.c_str(), static_cast<void*>(cfgAdditionObs.fDptDisCutHigh));
       }
     }
     correctionsLoaded = true;
@@ -1289,6 +1297,10 @@ struct FlowTask {
     double weffEventWithinGap08 = 0., weffEventSquareWithinGap08 = 0.;
     double sumPtsquareWsquareWithinGap08 = 0., sumPtWsquareWithinGap08 = 0.;
     double nTracksCorrected = 0;
+    double mpt_sub1 = 0;
+    double mpt_sub1_weffEv = 0;
+    double mpt_sub3 = 0;
+    double mpt_sub3_weffEv = 0;
     int magnetfield = 0;
     float independent = cent;
     float nTracksUncorrected = 0;
@@ -1405,6 +1417,16 @@ struct FlowTask {
           weffEventWithinGap08 += weff;
           weffEventSquareWithinGap08 += weff * weff;
         }
+        if (cfgAdditionObs.cfgManualCk) {
+          if (track.eta() >= etagapsPtPt[0].first && track.eta() <= etagapsPtPt[0].second) {
+            mpt_sub1 += weff * track.pt();
+            mpt_sub1_weffEv += weff;
+          }
+          if (track.eta() >= etagapsPtPt[2].first && track.eta() <= etagapsPtPt[2].second) {
+            mpt_sub3 += weff * track.pt();
+            mpt_sub3_weffEv += weff;
+          }
+        }
       }
       if (cfgUserIO.cfgConsistentEventFlag && consistentEventVector.size() == 6) { // o2-linter: disable=magic-number (size match)
         acceptedTracks.nFull += 1;
@@ -1477,13 +1499,12 @@ struct FlowTask {
     if (weffEvent) {
       registry.fill(HIST("hMeanPt"), independent, ptSum / weffEvent, weffEvent);
     }
-    if (weffEventWithinGap08)
+    if (weffEventWithinGap08) {
       registry.fill(HIST("hMeanPtWithinGap08"), independent, ptSum_Gap08 / weffEventWithinGap08, cfgUserIO.cfgUserPtVnEvWeightEnabled ? weffEventWithinGap08 : 1.);
-    if (weffEventWithinGap08)
       bootstrapArray[sampleIndex][kMeanPtWithinGap08]->Fill(independent, ptSum_Gap08 / weffEventWithinGap08, 1.0);
-    // c22_gap8 * pt_withGap8
-    if (weffEventWithinGap08)
+      // c22_gap8 * pt_withGap8
       fillpTvnProfile(corrconfigs.at(7), ptSum_Gap08, weffEventWithinGap08, HIST("c22_gap08_Weff"), HIST("c22_gap08_trackMeanPt"), independent);
+    }
     // PtVariance
     if (weffEventDiffWithGap08) {
       registry.fill(HIST("PtVariance_partA_WithinGap08"), independent,
@@ -1494,6 +1515,25 @@ struct FlowTask {
                     weffEventDiffWithGap08);
     }
 
+    if (cfgAdditionObs.cfgManualCk) {
+      // 2pc event weight:
+      double ev2pc = mpt_sub1_weffEv * mpt_sub3_weffEv;
+      // manual pt-pt variance
+      if (mpt_sub1_weffEv) {
+        mpt_sub1 = mpt_sub1 / mpt_sub1_weffEv;
+        registry.fill(HIST("pt_1sub1_1pc"), independent, mpt_sub1, mpt_sub1_weffEv);
+      }
+      if (mpt_sub3_weffEv) {
+        mpt_sub3 = mpt_sub3 / mpt_sub3_weffEv;
+        registry.fill(HIST("pt_1sub3_1pc"), independent, mpt_sub3, mpt_sub3_weffEv);
+      }
+      if (mpt_sub1_weffEv && mpt_sub3_weffEv) {
+        registry.fill(HIST("ptpt_1sub1_1sub3_2pc"), independent, mpt_sub1 * mpt_sub3, ev2pc);
+        registry.fill(HIST("pt_1sub1_2pc"), independent, mpt_sub1, ev2pc);
+        registry.fill(HIST("pt_1sub3_2pc"), independent, mpt_sub3, ev2pc);
+      }
+    }
+
     // v02
     if (cfgAdditionObs.cfgV02Enabled && weffEventFrac > 0) {
       for (auto ipt = 0; ipt < fPtAxis->GetNbins(); ipt++) {
@@ -1569,9 +1609,8 @@ struct FlowTask {
           ptSum_Gap08 += mcParticle.pt();
           count_Gap08 += 1.;
         }
-      }
-      if (withinPtRef)
         fGFW->Fill(mcParticle.eta(), fPtAxis->FindBin(mcParticle.pt()) - 1, mcParticle.phi(), 1., 1);
+      }
       if (withinPtPOI)
         fGFW->Fill(mcParticle.eta(), fPtAxis->FindBin(mcParticle.pt()) - 1, mcParticle.phi(), 1., 2);
       if (withinPtPOI && withinPtRef)