diff --git a/include/boost/histogram/accumulators/mean.hpp b/include/boost/histogram/accumulators/mean.hpp
index 18dc84ba..f814fc04 100644
--- a/include/boost/histogram/accumulators/mean.hpp
+++ b/include/boost/histogram/accumulators/mean.hpp
@@ -37,11 +37,11 @@ public:
     sum_of_deltas_squared_ += delta * (x - mean_);
   }
 
-  void operator()(const RealType& w, const RealType& x) noexcept {
-    sum_ += w;
+  void operator()(const weight_type<RealType>& w, const RealType& x) noexcept {
+    sum_ += w.value;
     const auto delta = x - mean_;
-    mean_ += w * delta / sum_;
-    sum_of_deltas_squared_ += w * delta * (x - mean_);
+    mean_ += w.value * delta / sum_;
+    sum_of_deltas_squared_ += w.value * delta * (x - mean_);
   }
 
   template <class T>
diff --git a/include/boost/histogram/accumulators/weighted_mean.hpp b/include/boost/histogram/accumulators/weighted_mean.hpp
index 8bcc447d..6e4657f4 100644
--- a/include/boost/histogram/accumulators/weighted_mean.hpp
+++ b/include/boost/histogram/accumulators/weighted_mean.hpp
@@ -10,6 +10,7 @@
 #include <boost/assert.hpp>
 #include <boost/core/nvp.hpp>
 #include <boost/histogram/fwd.hpp> // for weighted_mean<>
+#include <boost/histogram/weight.hpp>
 #include <type_traits>
 
 namespace boost {
@@ -34,14 +35,14 @@ public:
       , sum_of_weighted_deltas_squared_(
             variance * (sum_of_weights_ - sum_of_weights_squared_ / sum_of_weights_)) {}
 
-  void operator()(const RealType& x) { operator()(1, x); }
+  void operator()(const RealType& x) { operator()(weight(1), x); }
 
-  void operator()(const RealType& w, const RealType& x) {
-    sum_of_weights_ += w;
-    sum_of_weights_squared_ += w * w;
+  void operator()(const weight_type<RealType>& w, const RealType& x) {
+    sum_of_weights_ += w.value;
+    sum_of_weights_squared_ += w.value * w.value;
     const auto delta = x - weighted_mean_;
-    weighted_mean_ += w * delta / sum_of_weights_;
-    sum_of_weighted_deltas_squared_ += w * delta * (x - weighted_mean_);
+    weighted_mean_ += w.value * delta / sum_of_weights_;
+    sum_of_weighted_deltas_squared_ += w.value * delta * (x - weighted_mean_);
   }
 
   template <typename T>
diff --git a/include/boost/histogram/detail/fill.hpp b/include/boost/histogram/detail/fill.hpp
index 3281532e..fbb04532 100644
--- a/include/boost/histogram/detail/fill.hpp
+++ b/include/boost/histogram/detail/fill.hpp
@@ -123,7 +123,7 @@ void fill_storage_4(mp11::mp_true, T&& t) noexcept {
 
 template <class T, class U>
 void fill_storage_4(mp11::mp_true, T&& t, U&& w) noexcept {
-  t += w;
+  t += w.value;
 }
 
 template <class T, class... Us>
@@ -136,7 +136,7 @@ template <class IW, class IS, class T, class U>
 void fill_storage_2(IW, IS, T&& t, U&& u) noexcept {
   mp11::tuple_apply(
       [&](auto&&... args) {
-        fill_storage_3(std::forward<T>(t), std::get<IW::value>(u).value, args...);
+        fill_storage_3(std::forward<T>(t), std::get<IW::value>(u), args...);
       },
       std::get<IS::value>(u).value);
 }
@@ -150,7 +150,7 @@ void fill_storage_2(mp11::mp_int<-1>, IS, T&& t, const U& u) noexcept {
 
 template <class IW, class T, class U>
 void fill_storage_2(IW, mp11::mp_int<-1>, T&& t, const U& u) noexcept {
-  fill_storage_3(std::forward<T>(t), std::get<IW::value>(u).value);
+  fill_storage_3(std::forward<T>(t), std::get<IW::value>(u));
 }
 
 template <class T, class U>
diff --git a/include/boost/histogram/detail/fill_n.hpp b/include/boost/histogram/detail/fill_n.hpp
index 9f63534b..35580b49 100644
--- a/include/boost/histogram/detail/fill_n.hpp
+++ b/include/boost/histogram/detail/fill_n.hpp
@@ -153,6 +153,17 @@ void fill_n_storage(S& s, const Index idx, Ts&&... p) noexcept {
   fold((p.second > 1 ? ++p.first : 0)...);
 }
 
+template <class S, class Index, class T, class... Ts>
+void fill_n_storage(S& s, const Index idx, weight_type<T>&& w, Ts&&... ps) noexcept {
+  if (is_valid(idx)) {
+    BOOST_ASSERT(idx < s.size());
+    fill_storage_3(s[idx], weight_type<decltype(*w.value.first)>{*w.value.first},
+                   *ps.first...);
+  }
+  if (w.value.second > 1) ++w.value.first;
+  fold((ps.second > 1 ? ++ps.first : 0)...);
+}
+
 // general Nd treatment
 template <class Index, class S, class A, class T, class... Ts>
 void fill_n_nd(const std::size_t offset, S& storage, A& axes, const std::size_t vsize,
@@ -259,6 +270,11 @@ void fill_n_check_extra_args(std::size_t n, Ts&&... ts) {
   fold(check(ts)...);
 }
 
+template <class T, class... Ts>
+void fill_n_check_extra_args(std::size_t n, weight_type<T>&& w, Ts&&... ts) {
+  fill_n_check_extra_args(n, w.value, std::forward<Ts>(ts)...);
+}
+
 inline void fill_n_check_extra_args(std::size_t) noexcept {}
 
 template <class S, class A, class T, std::size_t N, class... Us>
diff --git a/include/boost/histogram/histogram.hpp b/include/boost/histogram/histogram.hpp
index b86f49c7..f30b6328 100644
--- a/include/boost/histogram/histogram.hpp
+++ b/include/boost/histogram/histogram.hpp
@@ -15,8 +15,10 @@
 #include <boost/histogram/detail/mutex_base.hpp>
 #include <boost/histogram/detail/span.hpp>
 #include <boost/histogram/fwd.hpp>
+#include <boost/histogram/sample.hpp>
 #include <boost/histogram/storage_adaptor.hpp>
 #include <boost/histogram/unsafe_access.hpp>
+#include <boost/histogram/weight.hpp>
 #include <boost/mp11/list.hpp>
 #include <boost/throw_exception.hpp>
 #include <mutex>
@@ -214,7 +216,7 @@ public:
   void fill(const Iterable& args, const weight_type<T>& weights) {
     std::lock_guard<typename mutex_base_t::type> guard{mutex_base_t::get()};
     detail::fill_n(offset_, storage_, axes_, detail::make_span(args),
-                   detail::to_ptr_size(weights.value));
+                   weight(detail::to_ptr_size(weights.value)));
   }
 
   /** Fill histogram with several values and weights at once.
@@ -260,7 +262,7 @@ public:
     mp11::tuple_apply(
         [&](const auto&... sargs) {
           detail::fill_n(offset_, storage_, axes_, detail::make_span(args),
-                         detail::to_ptr_size(weights.value),
+                         weight(detail::to_ptr_size(weights.value)),
                          detail::to_ptr_size(sargs)...);
         },
         samples.value);
@@ -597,34 +599,6 @@ histogram(Iterable, S)
 
 #endif
 
-/** Helper function to mark argument as weight.
-
-  @param t argument to be forward to the histogram.
-*/
-template <typename T>
-auto weight(T&& t) noexcept {
-  return weight_type<T>{std::forward<T>(t)};
-}
-
-/** Helper function to mark arguments as sample.
-
-  @param ts arguments to be forwarded to the accumulator.
-*/
-template <typename... Ts>
-auto sample(Ts&&... ts) noexcept {
-  return sample_type<std::tuple<Ts...>>{std::forward_as_tuple(std::forward<Ts>(ts)...)};
-}
-
-template <class T>
-struct weight_type {
-  T value;
-};
-
-template <class T>
-struct sample_type {
-  T value;
-};
-
 } // namespace histogram
 } // namespace boost
 
diff --git a/include/boost/histogram/sample.hpp b/include/boost/histogram/sample.hpp
new file mode 100644
index 00000000..6289bd31
--- /dev/null
+++ b/include/boost/histogram/sample.hpp
@@ -0,0 +1,33 @@
+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_HISTOGRAM_SAMPLE_HPP
+#define BOOST_HISTOGRAM_SAMPLE_HPP
+
+#include <tuple>
+#include <utility>
+
+namespace boost {
+namespace histogram {
+
+template <class T>
+struct sample_type {
+  T value;
+};
+
+/** Helper function to mark arguments as sample.
+
+  @param ts arguments to be forwarded to the accumulator.
+*/
+template <class... Ts>
+auto sample(Ts&&... ts) noexcept {
+  return sample_type<std::tuple<Ts...>>{std::forward_as_tuple(std::forward<Ts>(ts)...)};
+}
+
+} // namespace histogram
+} // namespace boost
+
+#endif
diff --git a/include/boost/histogram/weight.hpp b/include/boost/histogram/weight.hpp
new file mode 100644
index 00000000..4054e469
--- /dev/null
+++ b/include/boost/histogram/weight.hpp
@@ -0,0 +1,36 @@
+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_HISTOGRAM_WEIGHT_HPP
+#define BOOST_HISTOGRAM_WEIGHT_HPP
+
+#include <utility>
+
+namespace boost {
+namespace histogram {
+
+template <class T>
+struct weight_type {
+  T value;
+  template <class U>
+  operator weight_type<U>() const {
+    return weight_type<U>{static_cast<U>(value)};
+  }
+};
+
+/** Helper function to mark argument as weight.
+
+  @param t argument to be forward to the histogram.
+*/
+template <class T>
+auto weight(T&& t) noexcept {
+  return weight_type<T>{std::forward<T>(t)};
+}
+
+} // namespace histogram
+} // namespace boost
+
+#endif
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index debac596..b81847b2 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -54,6 +54,18 @@ boost_test(TYPE compile-fail SOURCES make_histogram_fail0.cpp
 boost_test(TYPE compile-fail SOURCES make_histogram_fail1.cpp
   LIBRARIES Boost::histogram
 )
+boost_test(TYPE compile-fail SOURCES profile_fail0.cpp
+  LIBRARIES Boost::histogram
+)
+boost_test(TYPE compile-fail SOURCES profile_fail1.cpp
+  LIBRARIES Boost::histogram
+)
+boost_test(TYPE compile-fail SOURCES profile_fail2.cpp
+  LIBRARIES Boost::histogram
+)
+boost_test(TYPE compile-fail SOURCES profile_fail3.cpp
+  LIBRARIES Boost::histogram
+)
 boost_test(TYPE run SOURCES accumulators_test.cpp
   LIBRARIES Boost::histogram Boost::core)
 boost_test(TYPE run SOURCES algorithm_project_test.cpp
diff --git a/test/Jamfile b/test/Jamfile
index 5616e585..72586691 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -101,6 +101,10 @@ alias failure :
     [ compile-fail axis_variable_fail1.cpp ]
     [ compile-fail make_histogram_fail0.cpp ]
     [ compile-fail make_histogram_fail1.cpp ]
+    [ compile-fail profile_fail0.cpp ]
+    [ compile-fail profile_fail1.cpp ]
+    [ compile-fail profile_fail2.cpp ]
+    [ compile-fail profile_fail3.cpp ]
     ;
 
 alias threading :
diff --git a/test/accumulators_serialization_test.cpp b/test/accumulators_serialization_test.cpp
index 50530503..b97ff6bf 100644
--- a/test/accumulators_serialization_test.cpp
+++ b/test/accumulators_serialization_test.cpp
@@ -8,6 +8,7 @@
 #include <boost/core/lightweight_test.hpp>
 #include <boost/histogram/accumulators.hpp>
 #include <boost/histogram/serialization.hpp>
+#include <boost/histogram/weight.hpp>
 #include "throw_exception.hpp"
 #include "utility_serialization.hpp"
 
@@ -31,7 +32,7 @@ int main(int argc, char** argv) {
     const auto filename = join(argv[1], "accumulators_serialization_test_mean.xml");
     accumulators::mean<> a;
     a(1);
-    a(0.5, 2);
+    a(weight(0.5), 2);
     a(3);
     print_xml(filename, a);
 
@@ -61,7 +62,7 @@ int main(int argc, char** argv) {
         join(argv[1], "accumulators_serialization_test_weighted_mean.xml");
     accumulators::weighted_mean<> a;
     a(1);
-    a(0.5, 2);
+    a(weight(0.5), 2);
     a(3);
     print_xml(filename, a);
 
diff --git a/test/accumulators_test.cpp b/test/accumulators_test.cpp
index 511b82e2..69177685 100644
--- a/test/accumulators_test.cpp
+++ b/test/accumulators_test.cpp
@@ -11,6 +11,7 @@
 #include <boost/histogram/accumulators/thread_safe.hpp>
 #include <boost/histogram/accumulators/weighted_mean.hpp>
 #include <boost/histogram/accumulators/weighted_sum.hpp>
+#include <boost/histogram/weight.hpp>
 #include <sstream>
 #include "is_close.hpp"
 #include "throw_exception.hpp"
@@ -114,10 +115,10 @@ int main() {
 
     // also same as feeding all samples twice
     m_t d;
-    d(2, 4);
-    d(2, 7);
-    d(2, 13);
-    d(2, 16);
+    d(weight(2), 4);
+    d(weight(2), 7);
+    d(weight(2), 13);
+    d(weight(2), 16);
 
     BOOST_TEST_EQ(d, c);
 
@@ -132,9 +133,9 @@ int main() {
     BOOST_TEST_EQ(a.sum_of_weights(), 0);
     BOOST_TEST_EQ(a, m_t{});
 
-    a(0.5, 1);
-    a(1.0, 2);
-    a(0.5, 3);
+    a(weight(0.5), 1);
+    a(weight(1.0), 2);
+    a(weight(0.5), 3);
 
     BOOST_TEST_EQ(a.sum_of_weights(), 2);
     BOOST_TEST_EQ(a.sum_of_weights_squared(), 1.5);
diff --git a/test/algorithm_empty_test.cpp b/test/algorithm_empty_test.cpp
index 0c15894e..f3787f04 100644
--- a/test/algorithm_empty_test.cpp
+++ b/test/algorithm_empty_test.cpp
@@ -21,92 +21,40 @@ template <typename Tag>
 void run_tests() {
   auto ax = axis::integer<>(0, 10);
 
-  auto h1 = make(Tag(), ax);
-  BOOST_TEST(empty(h1, coverage::all));
-  BOOST_TEST(empty(h1, coverage::inner));
-  for (int i = -1; i < 11; ++i) {
-    h1.reset();
-    h1(i);
-    BOOST_TEST(!empty(h1, coverage::all));
-    if (i == -1 || i == 10) {
-      BOOST_TEST(empty(h1, coverage::inner));
-    } else {
-      BOOST_TEST(!empty(h1, coverage::inner));
-    }
-  }
-
-  auto h2 = make_s(Tag(), std::vector<double>(), ax, ax);
-  BOOST_TEST(empty(h2, coverage::all));
-  BOOST_TEST(empty(h2, coverage::inner));
-  for (int i = -1; i < 11; ++i) {
-    for (int j = -1; j < 11; ++j) {
-      h2.reset();
-      h2(i, j);
-      BOOST_TEST(!empty(h2, coverage::all));
-
-      if ((i == -1 || i == 10) || (j == -1 || j == 10)) {
-        BOOST_TEST(empty(h2, coverage::inner));
+  {
+    auto h = make(Tag(), ax);
+    BOOST_TEST(empty(h, coverage::all));
+    BOOST_TEST(empty(h, coverage::inner));
+    for (int i = -1; i < 11; ++i) {
+      h.reset();
+      h(i);
+      BOOST_TEST(!empty(h, coverage::all));
+      if (i == -1 || i == 10) {
+        BOOST_TEST(empty(h, coverage::inner));
       } else {
-        BOOST_TEST(!empty(h2, coverage::inner));
+        BOOST_TEST(!empty(h, coverage::inner));
       }
     }
   }
 
-  /* BROKEN, SEE https://github.com/boostorg/histogram/issues/244
-  auto h3 = make_s(Tag(), std::array<int, 12>(), ax);
-  BOOST_TEST(empty(h3, coverage::all));
-  BOOST_TEST(empty(h3, coverage::inner));
-  h3(-2);
-  BOOST_TEST(!empty(h3, coverage::all));
-  BOOST_TEST(empty(h3, coverage::inner));
-  h3(2);
-  BOOST_TEST(!empty(h3, coverage::all));
-  BOOST_TEST(!empty(h3, coverage::inner));
-  */
-
-  auto h4 = make_s(Tag(), std::unordered_map<std::size_t, int>(), ax);
-  BOOST_TEST(empty(h4, coverage::all));
-  BOOST_TEST(empty(h4, coverage::inner));
-  h4(-2);
-  BOOST_TEST(!empty(h4, coverage::all));
-  BOOST_TEST(empty(h4, coverage::inner));
-  h4(2);
-  BOOST_TEST(!empty(h4, coverage::all));
-  BOOST_TEST(!empty(h4, coverage::inner));
-
-  auto h5 = make_s(Tag(), std::vector<accumulators::weighted_sum<>>(),
-                   axis::integer<>(0, 10), axis::integer<>(0, 10));
-  BOOST_TEST(empty(h5, coverage::all));
-  BOOST_TEST(empty(h5, coverage::inner));
-  h5.reset();
-  h5(weight(2), -2, -4);
-  BOOST_TEST(!empty(h5, coverage::all));
-  BOOST_TEST(empty(h5, coverage::inner));
-  h5.reset();
-  h5(weight(1), -4, 2);
-  BOOST_TEST(!empty(h5, coverage::all));
-  BOOST_TEST(empty(h5, coverage::inner));
-  h5.reset();
-  h5(weight(3), 3, 5);
-  BOOST_TEST(!empty(h5, coverage::all));
-  BOOST_TEST(!empty(h5, coverage::inner));
-
-  auto h6 = make_s(Tag(), std::vector<accumulators::weighted_mean<>>(),
-                   axis::integer<>(0, 10), axis::integer<>(0, 10));
-  BOOST_TEST(empty(h6, coverage::all));
-  BOOST_TEST(empty(h6, coverage::inner));
-  h6.reset();
-  h6(weight(2), -2, -4);
-  BOOST_TEST(!empty(h6, coverage::all));
-  BOOST_TEST(empty(h6, coverage::inner));
-  h6.reset();
-  h6(weight(1), -4, 2);
-  BOOST_TEST(!empty(h6, coverage::all));
-  BOOST_TEST(empty(h6, coverage::inner));
-  h6.reset();
-  h6(weight(3), 3, 5);
-  BOOST_TEST(!empty(h6, coverage::all));
-  BOOST_TEST(!empty(h6, coverage::inner));
+  {
+    auto h = make_s(Tag(), std::vector<accumulators::weighted_mean<>>(),
+                    axis::integer<>(0, 10), axis::integer<>(0, 10));
+    BOOST_TEST(empty(h, coverage::all));
+    BOOST_TEST(empty(h, coverage::inner));
+    h.reset();
+    h(weight(2), -2, -4, sample(3));
+    BOOST_TEST(!empty(h, coverage::all));
+    BOOST_TEST(empty(h, coverage::inner));
+    h.reset();
+    h(weight(1), -4, 2, sample(2));
+    BOOST_TEST(!empty(h, coverage::all));
+    BOOST_TEST(empty(h, coverage::inner));
+    h.reset();
+    h(weight(3), 3, 5, sample(1));
+    BOOST_TEST(!empty(h, coverage::all));
+    BOOST_TEST(!empty(h, coverage::inner));
+  }
 }
 
 int main() {
diff --git a/test/profile_fail0.cpp b/test/profile_fail0.cpp
new file mode 100644
index 00000000..d0d79b50
--- /dev/null
+++ b/test/profile_fail0.cpp
@@ -0,0 +1,14 @@
+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/histogram/axis/integer.hpp>
+#include <boost/histogram/make_profile.hpp>
+
+int main() {
+  using namespace boost::histogram;
+  auto h = make_profile(axis::integer<>(0, 5));
+  h(0, weight(1)); // profile requires a sample
+}
diff --git a/test/profile_fail1.cpp b/test/profile_fail1.cpp
new file mode 100644
index 00000000..2c9ea11f
--- /dev/null
+++ b/test/profile_fail1.cpp
@@ -0,0 +1,14 @@
+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/histogram/axis/integer.hpp>
+#include <boost/histogram/make_profile.hpp>
+
+int main() {
+  using namespace boost::histogram;
+  auto h = make_profile(axis::integer<>(0, 5));
+  h(0, sample(1, 2)); // profile requires one sample
+}
diff --git a/test/profile_fail2.cpp b/test/profile_fail2.cpp
new file mode 100644
index 00000000..485f0a51
--- /dev/null
+++ b/test/profile_fail2.cpp
@@ -0,0 +1,14 @@
+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/histogram/axis/integer.hpp>
+#include <boost/histogram/make_profile.hpp>
+
+int main() {
+  using namespace boost::histogram;
+  auto h = make_weighted_profile(axis::integer<>(0, 5));
+  h(0); // weighted profile requires a sample
+}
diff --git a/test/profile_fail3.cpp b/test/profile_fail3.cpp
new file mode 100644
index 00000000..f9fc61a5
--- /dev/null
+++ b/test/profile_fail3.cpp
@@ -0,0 +1,14 @@
+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/histogram/axis/integer.hpp>
+#include <boost/histogram/make_profile.hpp>
+
+int main() {
+  using namespace boost::histogram;
+  auto h = make_profile(axis::integer<>(0, 5));
+  h(0, sample(1, 2)); // weighted profile requires one sample
+}
diff --git a/test/storage_adaptor_test.cpp b/test/storage_adaptor_test.cpp
index 4b99cab3..6f8e01f5 100644
--- a/test/storage_adaptor_test.cpp
+++ b/test/storage_adaptor_test.cpp
@@ -8,9 +8,9 @@
 #include <boost/core/lightweight_test.hpp>
 #include <boost/histogram/accumulators/weighted_mean.hpp>
 #include <boost/histogram/accumulators/weighted_sum.hpp>
-#include "throw_exception.hpp"
 #include <boost/histogram/storage_adaptor.hpp>
 #include <boost/histogram/unlimited_storage.hpp>
+#include <boost/histogram/weight.hpp>
 #include <cmath>
 #include <deque>
 #include <limits>
@@ -18,6 +18,7 @@
 #include <sstream>
 #include <vector>
 #include "is_close.hpp"
+#include "throw_exception.hpp"
 #include "utility_allocator.hpp"
 
 using namespace boost::histogram;
@@ -230,7 +231,7 @@ int main() {
     auto a = storage_adaptor<std::vector<accumulators::weighted_mean<double>>>();
     a.reset(1);
     a[0](/* sample */ 1);
-    a[0](/* weight */ 2, /* sample */ 2);
+    a[0](weight(2), /* sample */ 2);
     a[0] += accumulators::weighted_mean<>(1, 0, 0, 0);
     BOOST_TEST_EQ(a[0].sum_of_weights(), 4);
     BOOST_TEST_IS_CLOSE(a[0].value(), 1.25, 1e-3);