diff --git a/CMakeLists.txt b/CMakeLists.txt
index df41ae8..0ab1e73 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -419,6 +419,7 @@ if(AARE_TESTS)
             ${CMAKE_CURRENT_SOURCE_DIR}/src/ClusterFinder.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/ClusterVector.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/Cluster.test.cpp
+            ${CMAKE_CURRENT_SOURCE_DIR}/src/CalculateEta.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/ClusterFile.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/Pedestal.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/NumpyFile.test.cpp
diff --git a/include/aare/CalculateEta.hpp b/include/aare/CalculateEta.hpp
index 088b4e8..86871c9 100644
--- a/include/aare/CalculateEta.hpp
+++ b/include/aare/CalculateEta.hpp
@@ -25,12 +25,11 @@ typedef enum {
     pTopRight = 8
 } pixel;
 
-// TODO: maybe template this!!!!!! why int32_t????
-struct Eta2 {
+template <typename T> struct Eta2 {
     double x;
     double y;
     int c;
-    int32_t sum;
+    T sum;
 };
 
 /**
@@ -56,9 +55,9 @@ NDArray<double, 2> calculate_eta2(const ClusterVector<ClusterType> &clusters) {
  */
 template <typename T, uint8_t ClusterSizeX, uint8_t ClusterSizeY,
           typename CoordType>
-Eta2 calculate_eta2(
-    const Cluster<T, ClusterSizeX, ClusterSizeY, CoordType> &cl) {
-    Eta2 eta{};
+Eta2<T>
+calculate_eta2(const Cluster<T, ClusterSizeX, ClusterSizeY, CoordType> &cl) {
+    Eta2<T> eta{};
 
     auto max_sum = cl.max_sum_2x2();
     eta.sum = max_sum.first;
@@ -67,7 +66,7 @@ Eta2 calculate_eta2(
     size_t index_bottom_left_max_2x2_subcluster =
         (int(c / (ClusterSizeX - 1))) * ClusterSizeX + c % (ClusterSizeX - 1);
 
-    if ((cl.data[index_bottom_left_max_2x2_subcluster] +s
+    if ((cl.data[index_bottom_left_max_2x2_subcluster] +
          cl.data[index_bottom_left_max_2x2_subcluster + 1]) != 0)
         eta.x = static_cast<double>(
                     cl.data[index_bottom_left_max_2x2_subcluster + 1]) /
@@ -89,9 +88,9 @@ Eta2 calculate_eta2(
 
 // calculates Eta3 for 3x3 cluster based on code from analyze_cluster
 // TODO only supported for 3x3 Clusters
-template <typename T> Eta2 calculate_eta3(const Cluster<T, 3, 3> &cl) {
+template <typename T> Eta2<T> calculate_eta3(const Cluster<T, 3, 3> &cl) {
 
-    Eta2 eta{};
+    Eta2<T> eta{};
 
     T sum = 0;
 
diff --git a/src/CalculateEta.test.cpp b/src/CalculateEta.test.cpp
new file mode 100644
index 0000000..2bdf387
--- /dev/null
+++ b/src/CalculateEta.test.cpp
@@ -0,0 +1,62 @@
+/************************************************
+ * @file CalculateEta.test.cpp
+ * @short test case to calculate_eta2
+ ***********************************************/
+
+#include "aare/CalculateEta.hpp"
+#include "aare/Cluster.hpp"
+#include "aare/ClusterFile.hpp"
+
+// #include "catch.hpp"
+#include <array>
+#include <catch2/catch_all.hpp>
+#include <catch2/catch_test_macros.hpp>
+
+using namespace aare;
+
+using ClusterTypes =
+    std::variant<Cluster<int, 2, 2>, Cluster<int, 3, 3>, Cluster<int, 5, 5>,
+                 Cluster<int, 4, 2>, Cluster<int, 2, 3>>;
+
+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, corner::cBottomLeft, 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, corner::cTopRight, 20}),
+        std::make_tuple(ClusterTypes{Cluster<int, 5, 5>{
+                            0, 0, {1, 6, 7, 6, 5, 4, 3, 2, 1, 8, 8, 9, 2,
+                                   1, 4, 5, 6, 7, 8, 4, 1, 1, 1, 1, 1}}},
+                        Eta2<int>{9. / 17, 5. / 13, 8, 28}),
+        std::make_tuple(
+            ClusterTypes{Cluster<int, 4, 2>{0, 0, {1, 4, 7, 2, 5, 6, 4, 3}}},
+            Eta2<int>{7. / 11, 6. / 10, 1, 21}),
+        std::make_tuple(
+            ClusterTypes{Cluster<int, 2, 3>{0, 0, {1, 3, 2, 3, 4, 2}}},
+            Eta2<int>{3. / 5, 4. / 6, 1, 11}));
+}
+
+TEST_CASE("compute_largest_2x2_subcluster", "[.eta_calculation]") {
+    auto [cluster, expected_eta] = get_test_parameters();
+
+    auto [sum, index] = std::visit(
+        [](const auto &clustertype) { return clustertype.max_sum_2x2(); },
+        cluster);
+    CHECK(expected_eta.c == index);
+    CHECK(expected_eta.sum == sum);
+}
+
+TEST_CASE("calculate_eta2", "[.eta_calculation]") {
+
+    auto [cluster, expected_eta] = get_test_parameters();
+
+    auto eta = std::visit(
+        [](const auto &clustertype) { return calculate_eta2(clustertype); },
+        cluster);
+
+    CHECK(eta.x == expected_eta.x);
+    CHECK(eta.y == expected_eta.y);
+    CHECK(eta.c == expected_eta.c);
+    CHECK(eta.sum == expected_eta.sum);
+}
diff --git a/src/Cluster.test.cpp b/src/Cluster.test.cpp
index 7918d72..e502012 100644
--- a/src/Cluster.test.cpp
+++ b/src/Cluster.test.cpp
@@ -26,36 +26,3 @@ TEST_CASE("Correct Instantiation of Cluster and ClusterVector",
     CHECK(not is_cluster_v<int>);
     CHECK(is_cluster_v<Cluster<int, 3, 3>>);
 }
-
-using ClusterTypes =
-    std::variant<Cluster<int, 2, 2>, Cluster<int, 3, 3>, Cluster<int, 5, 5>,
-                 Cluster<int, 4, 2>, Cluster<int, 2, 3>>;
-
-TEST_CASE("calculate_eta2", "[.cluster][.eta_calculation]") {
-
-    auto [cluster, expected_eta] = GENERATE(
-        std::make_tuple(ClusterTypes{Cluster<int, 2, 2>{0, 0, {1, 2, 3, 1}}},
-                        Eta2{2. / 3, 3. / 4, corner::cBottomLeft, 7}),
-        std::make_tuple(
-            ClusterTypes{Cluster<int, 3, 3>{0, 0, {1, 2, 3, 4, 5, 6, 1, 2, 7}}},
-            Eta2{6. / 11, 2. / 7, corner::cTopRight, 20}),
-        std::make_tuple(ClusterTypes{Cluster<int, 5, 5>{
-                            0, 0, {1, 6, 7, 6, 5, 4, 3, 2, 1, 8, 8, 9, 2,
-                                   1, 4, 5, 6, 7, 8, 4, 1, 1, 1, 1, 1}}},
-                        Eta2{9. / 17, 5. / 13, 8, 28}),
-        std::make_tuple(
-            ClusterTypes{Cluster<int, 4, 2>{0, 0, {1, 4, 7, 2, 5, 6, 4, 3}}},
-            Eta2{7. / 11, 6. / 10, 1, 21}),
-        std::make_tuple(
-            ClusterTypes{Cluster<int, 2, 3>{0, 0, {1, 3, 2, 3, 4, 2}}},
-            Eta2{3. / 5, 4. / 6, 1, 11}));
-
-    Eta2 eta = std::visit(
-        [](const auto &clustertype) { return calculate_eta2(clustertype); },
-        cluster);
-
-    CHECK(eta.x == expected_eta.x);
-    CHECK(eta.y == expected_eta.y);
-    CHECK(eta.c == expected_eta.c);
-    CHECK(eta.sum == expected_eta.sum);
-}
diff --git a/src/Interpolator.cpp b/src/Interpolator.cpp
index e434231..e4f8e5c 100644
--- a/src/Interpolator.cpp
+++ b/src/Interpolator.cpp
@@ -68,7 +68,7 @@ Interpolator::interpolate(const ClusterVector<ClusterType> &clusters) {
         for (size_t i = 0; i < clusters.size(); i++) {
 
             auto cluster = clusters.at(i);
-            Eta2 eta = calculate_eta2(cluster);
+            auto eta = calculate_eta2(cluster);
 
             Photon photon;
             photon.x = cluster.x;
@@ -118,7 +118,7 @@ Interpolator::interpolate(const ClusterVector<ClusterType> &clusters) {
                clusters.cluster_size_y() == 2) {
         for (size_t i = 0; i < clusters.size(); i++) {
             auto cluster = clusters.at(i);
-            Eta2 eta = calculate_eta2(cluster);
+            auto eta = calculate_eta2(cluster);
 
             Photon photon;
             photon.x = cluster.x;