diff --git a/README.md b/README.md
index 6c36775..119c3b0 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,10 @@
 # aare
 Data analysis library for PSI hybrid detectors
 
+## Documentation 
+
+Detailed documentation including installation can be found in [Documentation](https://slsdetectorgroup.github.io/aare/)
+
 
 ## Build and install
 
diff --git a/RELEASE.md b/RELEASE.md
index 7f7fed8..4b69ecd 100644
--- a/RELEASE.md
+++ b/RELEASE.md
@@ -1,5 +1,13 @@
 # Release notes
 
+### 2025.10.27
+
+Features: 
+
+- max_sum_2x2 including index of subcluster with highest energy is now available from Python API 
+- eta stores corner as enum class cTopLeft, cTopRight, BottomLeft, cBottomRight indicating 2x2 subcluster with largest energy relative to cluster center 
+- max_sum_2x2 returns corner as index
+
 ### 2025.10.1
 
 Bugfixes: 
diff --git a/include/aare/CalculateEta.hpp b/include/aare/CalculateEta.hpp
index 6df263a..93902fa 100644
--- a/include/aare/CalculateEta.hpp
+++ b/include/aare/CalculateEta.hpp
@@ -3,16 +3,10 @@
 #include "aare/Cluster.hpp"
 #include "aare/ClusterVector.hpp"
 #include "aare/NDArray.hpp"
+#include "aare/defs.hpp"
 
 namespace aare {
 
-enum class corner : int {
-    cTopLeft = 0,
-    cTopRight = 1,
-    cBottomLeft = 2,
-    cBottomRight = 3
-};
-
 enum class pixel : int {
     pBottomLeft = 0,
     pBottom = 1,
@@ -28,7 +22,7 @@ enum class pixel : int {
 template <typename T> struct Eta2 {
     double x;
     double y;
-    int c{0};
+    corner c{0};
     T sum;
 };
 
@@ -66,11 +60,11 @@ calculate_eta2(const Cluster<T, ClusterSizeX, ClusterSizeY, CoordType> &cl) {
         (ClusterSizeX / 2) + (ClusterSizeY / 2) * ClusterSizeX;
 
     auto max_sum = cl.max_sum_2x2();
-    eta.sum = max_sum.first;
-    int c = max_sum.second;
+    eta.sum = max_sum.sum;
+    corner c = max_sum.index;
 
     // subcluster top right from center
-    switch (static_cast<corner>(c)) {
+    switch (c) {
     case (corner::cTopLeft):
         if ((cl.data[cluster_center_index - 1] +
              cl.data[cluster_center_index]) != 0)
diff --git a/include/aare/Cluster.hpp b/include/aare/Cluster.hpp
index a4d2428..f0507d2 100755
--- a/include/aare/Cluster.hpp
+++ b/include/aare/Cluster.hpp
@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include "defs.hpp"
 #include <algorithm>
 #include <array>
 #include <cstdint>
@@ -45,7 +46,7 @@ struct Cluster {
      * @return photon energy of subcluster, 2x2 subcluster index relative to
      * cluster center
      */
-    std::pair<T, int> max_sum_2x2() const {
+    Sum_index_pair<T, corner> max_sum_2x2() const {
 
         if constexpr (cluster_size_x == 3 && cluster_size_y == 3) {
             std::array<T, 4> sum_2x2_subclusters;
@@ -56,9 +57,11 @@ struct Cluster {
             int index = std::max_element(sum_2x2_subclusters.begin(),
                                          sum_2x2_subclusters.end()) -
                         sum_2x2_subclusters.begin();
-            return std::make_pair(sum_2x2_subclusters[index], index);
+            return Sum_index_pair<T, corner>{sum_2x2_subclusters[index],
+                                             corner{index}};
         } else if constexpr (cluster_size_x == 2 && cluster_size_y == 2) {
-            return std::make_pair(data[0] + data[1] + data[2] + data[3], 0);
+            return Sum_index_pair<T, corner>{
+                data[0] + data[1] + data[2] + data[3], corner{0}};
         } else {
             constexpr size_t cluster_center_index =
                 (ClusterSizeX / 2) + (ClusterSizeY / 2) * ClusterSizeX;
@@ -97,7 +100,8 @@ struct Cluster {
             int index = std::max_element(sum_2x2_subcluster.begin(),
                                          sum_2x2_subcluster.end()) -
                         sum_2x2_subcluster.begin();
-            return std::make_pair(sum_2x2_subcluster[index], index);
+            return Sum_index_pair<T, corner>{sum_2x2_subcluster[index],
+                                             corner{index}};
         }
     }
 };
@@ -125,8 +129,8 @@ reduce_to_2x2(const Cluster<T, ClusterSizeX, ClusterSizeY, CoordType> &c) {
         (ClusterSizeX / 2) + (ClusterSizeY / 2) * ClusterSizeX;
 
     int16_t index_bottom_left_max_2x2_subcluster =
-        (int(index / (ClusterSizeX - 1))) * ClusterSizeX +
-        index % (ClusterSizeX - 1);
+        (int(static_cast<int>(index) / (ClusterSizeX - 1))) * ClusterSizeX +
+        static_cast<int>(index) % (ClusterSizeX - 1);
 
     result.x =
         c.x + (index_bottom_left_max_2x2_subcluster - cluster_center_index) %
@@ -149,22 +153,22 @@ Cluster<T, 2, 2, int16_t> reduce_to_2x2(const Cluster<T, 3, 3, int16_t> &c) {
 
     auto [s, i] = c.max_sum_2x2();
     switch (i) {
-    case 0:
+    case corner::cTopLeft:
         result.x = c.x - 1;
         result.y = c.y + 1;
         result.data = {c.data[0], c.data[1], c.data[3], c.data[4]};
         break;
-    case 1:
+    case corner::cTopRight:
         result.x = c.x;
         result.y = c.y + 1;
         result.data = {c.data[1], c.data[2], c.data[4], c.data[5]};
         break;
-    case 2:
+    case corner::cBottomLeft:
         result.x = c.x - 1;
         result.y = c.y;
         result.data = {c.data[3], c.data[4], c.data[6], c.data[7]};
         break;
-    case 3:
+    case corner::cBottomRight:
         result.x = c.x;
         result.y = c.y;
         result.data = {c.data[4], c.data[5], c.data[7], c.data[8]};
diff --git a/include/aare/ClusterCollector.hpp b/include/aare/ClusterCollector.hpp
index ae78a8e..a1cbcff 100644
--- a/include/aare/ClusterCollector.hpp
+++ b/include/aare/ClusterCollector.hpp
@@ -5,6 +5,7 @@
 #include "aare/ClusterFinderMT.hpp"
 #include "aare/ClusterVector.hpp"
 #include "aare/ProducerConsumerQueue.hpp"
+#include "aare/defs.hpp"
 
 namespace aare {
 
diff --git a/include/aare/ClusterFile.hpp b/include/aare/ClusterFile.hpp
index ccdace3..1295252 100644
--- a/include/aare/ClusterFile.hpp
+++ b/include/aare/ClusterFile.hpp
@@ -453,8 +453,8 @@ bool ClusterFile<ClusterType, Enable>::is_selected(ClusterType &cl) {
 
     if (m_noise_map) {
         auto sum_1x1 = cl.data[cluster_center_index]; // central pixel
-        auto sum_2x2 = cl.max_sum_2x2().first; // highest sum of 2x2 subclusters
-        auto total_sum = cl.sum();             // sum of all pixels
+        auto sum_2x2 = cl.max_sum_2x2().sum; // highest sum of 2x2 subclusters
+        auto total_sum = cl.sum();           // sum of all pixels
 
         auto noise =
             (*m_noise_map)(cl.y, cl.x); // TODO! check if this is correct
diff --git a/include/aare/ClusterVector.hpp b/include/aare/ClusterVector.hpp
index 00f4d25..9da5392 100644
--- a/include/aare/ClusterVector.hpp
+++ b/include/aare/ClusterVector.hpp
@@ -86,15 +86,14 @@ class ClusterVector<Cluster<T, ClusterSizeX, ClusterSizeY, CoordType>> {
     /**
      * @brief Sum the pixels in the 2x2 subcluster with the biggest pixel sum in
      * each cluster
-     * @return std::vector<T> vector of sums for each cluster
+     * @return vector of sums index pairs for each cluster
      */
-    std::vector<T> sum_2x2() {
-        std::vector<T> sums_2x2(m_data.size());
+    std::vector<Sum_index_pair<T, corner>> sum_2x2() {
+        std::vector<Sum_index_pair<T, corner>> sums_2x2(m_data.size());
 
-        std::transform(m_data.begin(), m_data.end(), sums_2x2.begin(),
-                       [](const ClusterType &cluster) {
-                           return cluster.max_sum_2x2().first;
-                       });
+        std::transform(
+            m_data.begin(), m_data.end(), sums_2x2.begin(),
+            [](const ClusterType &cluster) { return cluster.max_sum_2x2(); });
 
         return sums_2x2;
     }
diff --git a/include/aare/defs.hpp b/include/aare/defs.hpp
index 7ae6269..041dbc9 100644
--- a/include/aare/defs.hpp
+++ b/include/aare/defs.hpp
@@ -331,6 +331,19 @@ enum DACIndex {
     SLOW_ADC_TEMP
 };
 
+// helper pair class to easily expose in python
+template <typename T1, typename T2> struct Sum_index_pair {
+    T1 sum;
+    T2 index;
+};
+
+enum class corner : int {
+    cTopLeft = 0,
+    cTopRight = 1,
+    cBottomLeft = 2,
+    cBottomRight = 3
+};
+
 enum class TimingMode { Auto, Trigger };
 enum class FrameDiscardPolicy { NoDiscard, Discard, DiscardPartial };
 
diff --git a/python/src/bind_Cluster.hpp b/python/src/bind_Cluster.hpp
index b6f4272..c672a95 100644
--- a/python/src/bind_Cluster.hpp
+++ b/python/src/bind_Cluster.hpp
@@ -58,7 +58,17 @@ void define_Cluster(py::module &m, const std::string &typestr) {
                       &Cluster<Type, ClusterSizeX, ClusterSizeY, CoordType>::x)
 
         .def_readonly("y",
-                      &Cluster<Type, ClusterSizeX, ClusterSizeY, CoordType>::y);
+                      &Cluster<Type, ClusterSizeX, ClusterSizeY, CoordType>::y)
+
+        .def(
+            "max_sum_2x2",
+            [](Cluster<Type, ClusterSizeX, ClusterSizeY, CoordType> &self) {
+                auto max_sum = self.max_sum_2x2();
+                return py::make_tuple(max_sum.sum,
+                                      static_cast<int>(max_sum.index));
+            },
+            R"(calculates sum of 2x2 subcluster with highest energy and index relative to cluster center 0: top_left, 1: top_right, 2: bottom_left, 3: bottom_right
+            )");
 }
 
 template <typename T, uint8_t ClusterSizeX, uint8_t ClusterSizeY,
diff --git a/python/src/bind_ClusterVector.hpp b/python/src/bind_ClusterVector.hpp
index 597ae5f..662cd49 100644
--- a/python/src/bind_ClusterVector.hpp
+++ b/python/src/bind_ClusterVector.hpp
@@ -44,11 +44,16 @@ void define_ClusterVector(py::module &m, const std::string &typestr) {
                  auto *vec = new std::vector<Type>(self.sum());
                  return return_vector(vec);
              })
-        .def("sum_2x2",
-             [](ClusterVector<ClusterType> &self) {
-                 auto *vec = new std::vector<Type>(self.sum_2x2());
-                 return return_vector(vec);
-             })
+        .def(
+            "sum_2x2",
+            [](ClusterVector<ClusterType> &self) {
+                auto *vec = new std::vector<Sum_index_pair<Type, corner>>(
+                    self.sum_2x2());
+
+                return return_vector(vec);
+            },
+            R"(calculates sum of 2x2 subcluster with highest energy and index relative to cluster center 0: top_left, 1: top_right, 2: bottom_left, 3: bottom_right
+            )")
         .def_property_readonly("size", &ClusterVector<ClusterType>::size)
         .def("item_size", &ClusterVector<ClusterType>::item_size)
         .def_property_readonly("fmt",
diff --git a/python/src/module.cpp b/python/src/module.cpp
index 5de2fef..5005fc6 100644
--- a/python/src/module.cpp
+++ b/python/src/module.cpp
@@ -114,4 +114,11 @@ PYBIND11_MODULE(_aare, m) {
     reduce_to_3x3<int, 9, 9, uint16_t>(m);
     reduce_to_3x3<double, 9, 9, uint16_t>(m);
     reduce_to_3x3<float, 9, 9, uint16_t>(m);
+
+    using Sum_index_pair_d = Sum_index_pair<double, corner>;
+    PYBIND11_NUMPY_DTYPE(Sum_index_pair_d, sum, index);
+    using Sum_index_pair_f = Sum_index_pair<float, corner>;
+    PYBIND11_NUMPY_DTYPE(Sum_index_pair_f, sum, index);
+    using Sum_index_pair_i = Sum_index_pair<int, corner>;
+    PYBIND11_NUMPY_DTYPE(Sum_index_pair_i, sum, index);
 }
diff --git a/python/tests/test_Cluster.py b/python/tests/test_Cluster.py
index 6d2106d..578c97f 100644
--- a/python/tests/test_Cluster.py
+++ b/python/tests/test_Cluster.py
@@ -86,6 +86,17 @@ def test_calculate_eta():
     assert eta2[1,0] == 0.5
     assert eta2[1,1] == 0.4 #2/5
 
+
+def test_max_sum(): 
+    """Max 2x2 Sum"""
+    cluster = _aare.Cluster3x3i(5,5,np.array([1, 1, 1, 2, 3, 1, 2, 2, 1], dtype=np.int32))
+
+    max_sum = cluster.max_sum_2x2()
+
+    assert max_sum[0] == 9
+    assert max_sum[1] == 2
+
+
 def test_cluster_finder(): 
     """Test ClusterFinder""" 
 
diff --git a/python/tests/test_ClusterVector.py b/python/tests/test_ClusterVector.py
index fa98e3f..5d99778 100644
--- a/python/tests/test_ClusterVector.py
+++ b/python/tests/test_ClusterVector.py
@@ -32,6 +32,18 @@ def test_push_back_on_cluster_vector():
     assert arr[0]['y'] == 22
 
 
+def test_max_2x2_sum(): 
+    """max_2x2_sum"""
+    cv = _aare.ClusterVector_Cluster3x3i()
+    cv.push_back(_aare.Cluster3x3i(19, 22, np.array([0,1,0,2,3,0,2,1,0], dtype=np.int32)))
+    cv.push_back(_aare.Cluster3x3i(19, 22, np.ones(9, dtype=np.int32)))
+    assert cv.size == 2
+    max_2x2 = cv.sum_2x2()
+    assert max_2x2.size == 2
+    assert max_2x2[0]["sum"] == 8
+    assert max_2x2[0]["index"] == 2
+
+
 def test_make_a_hitmap_from_cluster_vector():
     cv = _aare.ClusterVector_Cluster3x3i()
 
diff --git a/src/CalculateEta.test.cpp b/src/CalculateEta.test.cpp
index 820ab44..f7cb304 100644
--- a/src/CalculateEta.test.cpp
+++ b/src/CalculateEta.test.cpp
@@ -21,22 +21,20 @@ using ClusterTypes =
 auto get_test_parameters() {
     return GENERATE(
         std::make_tuple(ClusterTypes{Cluster<int, 2, 2>{0, 0, {1, 2, 3, 1}}},
-                        Eta2<int>{2. / 3, 3. / 4,
-                                  static_cast<int>(corner::cBottomLeft), 7}),
+                        Eta2<int>{2. / 3, 3. / 4, corner::cTopLeft, 7}),
         std::make_tuple(
             ClusterTypes{Cluster<int, 3, 3>{0, 0, {1, 2, 3, 4, 5, 6, 1, 2, 7}}},
-            Eta2<int>{6. / 11, 2. / 7, static_cast<int>(corner::cTopRight),
-                      20}),
+            Eta2<int>{6. / 11, 2. / 7, corner::cBottomRight, 20}),
         std::make_tuple(ClusterTypes{Cluster<int, 5, 5>{
-                            0, 0, {1, 6, 7, 6, 5, 4, 3, 2, 1, 2, 8, 9, 8,
-                                   1, 4, 5, 6, 7, 8, 4, 1, 1, 1, 1, 1}}},
-                        Eta2<int>{8. / 17, 7. / 15, 9, 30}),
+                            0, 0, {1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 9, 8,
+                                   1, 4, 1, 6, 7, 8, 1, 1, 1, 1, 1, 1}}},
+                        Eta2<int>{8. / 17, 7. / 15, corner::cBottomLeft, 30}),
         std::make_tuple(
             ClusterTypes{Cluster<int, 4, 2>{0, 0, {1, 4, 7, 2, 5, 6, 4, 3}}},
-            Eta2<int>{4. / 10, 4. / 11, 1, 21}),
+            Eta2<int>{4. / 10, 4. / 11, corner::cTopLeft, 21}),
         std::make_tuple(
             ClusterTypes{Cluster<int, 2, 3>{0, 0, {1, 3, 2, 3, 4, 2}}},
-            Eta2<int>{3. / 5, 2. / 5, 1, 11}));
+            Eta2<int>{3. / 5, 2. / 5, corner::cBottomLeft, 11}));
 }
 
 TEST_CASE("compute_largest_2x2_subcluster", "[eta_calculation]") {
@@ -91,7 +89,7 @@ TEST_CASE("Calculate eta2 for a 3x3 int32 cluster with the largest 2x2 sum in "
     // 30, 23, 5
 
     auto eta = calculate_eta2(cl);
-    CHECK(eta.c == static_cast<int>(corner::cBottomLeft));
+    CHECK(eta.c == corner::cBottomLeft);
     CHECK(eta.x == 50.0 / (20 + 50)); // 4/(3+4)
     CHECK(eta.y == 50.0 / (23 + 50)); // 4/(1+4)
     CHECK(eta.sum == 30 + 23 + 20 + 50);
@@ -120,7 +118,7 @@ TEST_CASE("Calculate eta2 for a 3x3 int32 cluster with the largest 2x2 sum in "
     // 8, 12, 5
 
     auto eta = calculate_eta2(cl);
-    CHECK(eta.c == static_cast<int>(corner::cTopLeft));
+    CHECK(eta.c == corner::cTopLeft);
     CHECK(eta.x == 80. / (77 + 80));  // 4/(3+4)
     CHECK(eta.y == 91.0 / (91 + 80)); // 7/(7+4)
     CHECK(eta.sum == 77 + 80 + 82 + 91);