diff --git a/chrono_io.h b/chrono_io.h
new file mode 100644
index 0000000..3182c64
--- /dev/null
+++ b/chrono_io.h
@@ -0,0 +1,668 @@
+#ifndef CHRONO_IO_H
+#define CHRONO_IO_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that woud involve another several millennia of evolution).
+// We did not mean to shout.
+
+#include <chrono>
+#include <cstddef>
+#include <cstdint>
+#include <iosfwd>
+#include <ratio>
+#include <string>
+#include <type_traits>
+
+namespace date
+{
+
+namespace detail
+{
+
+#if __cplusplus >= 201402
+
+template <class CharT, std::size_t N>
+class string_literal
+{
+    CharT p_[N];
+
+public:
+    using const_iterator = const CharT*;
+
+    string_literal(string_literal const&) = default;
+    string_literal& operator=(string_literal const&) = delete;
+
+    template <std::size_t N1 = 2,
+              class = std::enable_if_t<N1 == N>>
+    constexpr string_literal(CharT c) noexcept
+        : p_{c}
+    {
+    }
+
+    constexpr string_literal(const CharT(&a)[N]) noexcept
+        : p_{}
+    {
+        for (std::size_t i = 0; i < N; ++i)
+            p_[i] = a[i];
+    }
+
+    template <class U = CharT, class = std::enable_if_t<1 < sizeof(U)>>
+    constexpr string_literal(const char(&a)[N]) noexcept
+        : p_{}
+    {
+        for (std::size_t i = 0; i < N; ++i)
+            p_[i] = a[i];
+    }
+
+    template <class CharT2, class = std::enable_if_t<!std::is_same<CharT2, CharT>{}>>
+    constexpr string_literal(string_literal<CharT2, N> const& a) noexcept
+        : p_{}
+    {
+        for (std::size_t i = 0; i < N; ++i)
+            p_[i] = a[i];
+    }
+
+    template <std::size_t N1, std::size_t N2,
+              class = std::enable_if_t<N1 + N2 - 1 == N>>
+    constexpr string_literal(const string_literal<CharT, N1>& x,
+                             const string_literal<CharT, N2>& y) noexcept
+        : p_{}
+    {
+        std::size_t i = 0;
+        for (; i < N1-1; ++i)
+            p_[i] = x[i];
+        for (std::size_t j = 0; j < N2; ++j, ++i)
+            p_[i] = y[j];
+    }
+
+    constexpr const CharT* data() const noexcept {return p_;}
+    constexpr std::size_t size() const noexcept {return N-1;}
+
+    constexpr const_iterator begin() const noexcept {return p_;}
+    constexpr const_iterator end()   const noexcept {return p_ + N-1;}
+
+    constexpr CharT const& operator[](std::size_t n) const noexcept
+    {
+        return p_[n];
+    }
+
+    template <class Traits>
+    friend
+    std::basic_ostream<CharT, Traits>&
+    operator<<(std::basic_ostream<CharT, Traits>& os, const string_literal& s)
+    {
+        return os << s.p_;
+    }
+};
+
+template <class CharT1, class CharT2, std::size_t N1, std::size_t N2>
+constexpr
+inline
+string_literal<std::conditional_t<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>,
+               N1 + N2 - 1>
+operator+(const string_literal<CharT1, N1>& x, const string_literal<CharT2, N2>& y) noexcept
+{
+    using CharT = std::conditional_t<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>;
+    return string_literal<CharT, N1 + N2 - 1>{string_literal<CharT, N1>{x},
+                                              string_literal<CharT, N2>{y}};
+}
+
+template <class CharT, std::size_t N>
+constexpr
+inline
+string_literal<CharT, N>
+msl(const CharT(&a)[N]) noexcept
+{
+    return string_literal<CharT, N>{a};
+}
+
+template <class CharT,
+          class = std::enable_if_t<std::is_same<CharT, char>{} ||
+                                   std::is_same<CharT, wchar_t>{} ||
+                                   std::is_same<CharT, char16_t>{} ||
+                                   std::is_same<CharT, char32_t>{}>>
+constexpr
+inline
+string_literal<CharT, 2>
+msl(CharT c) noexcept
+{
+    return string_literal<CharT, 2>{c};
+}
+
+constexpr
+std::size_t
+to_string_len(std::intmax_t i)
+{
+    std::size_t r = 0;
+    do
+    {
+        i /= 10;
+        ++r;
+    } while (i > 0);
+    return r;
+}
+
+template <std::intmax_t N>
+constexpr
+inline
+std::enable_if_t
+<
+    N < 10,
+    string_literal<char, to_string_len(N)+1>
+>
+msl() noexcept
+{
+    return msl(char(N % 10 + '0'));
+}
+
+template <std::intmax_t N>
+constexpr
+inline
+std::enable_if_t
+<
+    10 <= N,
+    string_literal<char, to_string_len(N)+1>
+>
+msl() noexcept
+{
+    return msl<N/10>() + msl(char(N % 10 + '0'));
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+constexpr
+inline
+std::enable_if_t
+<
+    std::ratio<N, D>::type::den != 1,
+    string_literal<CharT, to_string_len(std::ratio<N, D>::type::num) +
+                          to_string_len(std::ratio<N, D>::type::den) + 4>
+>
+msl(std::ratio<N, D>) noexcept
+{
+    using R = typename std::ratio<N, D>::type;
+    return msl(CharT{'['}) + msl<R::num>() + msl(CharT{'/'}) +
+                             msl<R::den>() + msl(CharT{']'});
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+constexpr
+inline
+std::enable_if_t
+<
+    std::ratio<N, D>::type::den == 1,
+    string_literal<CharT, to_string_len(std::ratio<N, D>::type::num) + 3>
+>
+msl(std::ratio<N, D>) noexcept
+{
+    using R = typename std::ratio<N, D>::type;
+    return msl(CharT{'['}) + msl<R::num>() + msl(CharT{']'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::atto) noexcept
+{
+    return msl(CharT{'a'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::femto) noexcept
+{
+    return msl(CharT{'f'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::pico) noexcept
+{
+    return msl(CharT{'p'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::nano) noexcept
+{
+    return msl(CharT{'n'});
+}
+
+template <class CharT>
+constexpr
+inline
+std::enable_if_t
+<
+    std::is_same<CharT, char>{},
+    string_literal<char, 3>
+>
+msl(std::micro) noexcept
+{
+    return string_literal<char, 3>{"\xC2\xB5"};
+}
+
+template <class CharT>
+constexpr
+inline
+std::enable_if_t
+<
+    !std::is_same<CharT, char>{},
+    string_literal<CharT, 2>
+>
+msl(std::micro) noexcept
+{
+    return string_literal<CharT, 2>{CharT{static_cast<unsigned char>('\xB5')}};
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::milli) noexcept
+{
+    return msl(CharT{'m'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::centi) noexcept
+{
+    return msl(CharT{'c'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::deci) noexcept
+{
+    return msl(CharT{'d'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::deca) noexcept
+{
+    return string_literal<CharT, 3>{"da"};
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::hecto) noexcept
+{
+    return msl(CharT{'h'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::kilo) noexcept
+{
+    return msl(CharT{'k'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::mega) noexcept
+{
+    return msl(CharT{'M'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::giga) noexcept
+{
+    return msl(CharT{'G'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::tera) noexcept
+{
+    return msl(CharT{'T'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::peta) noexcept
+{
+    return msl(CharT{'P'});
+}
+
+template <class CharT>
+constexpr
+inline
+auto
+msl(std::exa) noexcept
+{
+    return msl(CharT{'E'});
+}
+
+template <class CharT, class Rep, class Period>
+constexpr
+auto
+get_units(const std::chrono::duration<Rep, Period>&)
+{
+    return msl<CharT>(Period{}) + string_literal<CharT, 2>{"s"};
+}
+
+template <class CharT, class Rep>
+constexpr
+auto
+get_units(const std::chrono::duration<Rep, std::ratio<1>>&)
+{
+    return string_literal<CharT, 2>{"s"};
+}
+
+template <class CharT, class Rep>
+constexpr
+auto
+get_units(const std::chrono::duration<Rep, std::ratio<60>>&)
+{
+    return string_literal<CharT, 4>{"min"};
+}
+
+template <class CharT, class Rep>
+constexpr
+auto
+get_units(const std::chrono::duration<Rep, std::ratio<3600>>&)
+{
+    return string_literal<CharT, 2>{"h"};
+}
+
+#else  //  __cplusplus < 201402
+
+inline
+std::string
+to_string(std::uint64_t x)
+{
+    return std::to_string(x);
+}
+
+template <class CharT>
+std::basic_string<CharT>
+to_string(std::uint64_t x)
+{
+    auto y = std::to_string(x);
+    return std::basic_string<CharT>(y.begin(), y.end());
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+constexpr
+inline
+typename std::enable_if
+<
+    std::ratio<N, D>::type::den != 1,
+    std::basic_string<CharT>
+>::type
+msl(std::ratio<N, D>) noexcept
+{
+    using R = typename std::ratio<N, D>::type;
+    return std::basic_string<CharT>(1, '[') + to_string<CharT>(R::num) + CharT{'/'} +
+                                              to_string<CharT>(R::den) + CharT{']'};
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+constexpr
+inline
+typename std::enable_if
+<
+    std::ratio<N, D>::type::den == 1,
+    std::basic_string<CharT>
+>::type
+msl(std::ratio<N, D>) noexcept
+{
+    using R = typename std::ratio<N, D>::type;
+    return std::basic_string<CharT>(1, '[') + to_string<CharT>(R::num) + CharT{']'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::atto) noexcept
+{
+    return {1, 'a'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::femto) noexcept
+{
+    return {1, 'f'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::pico) noexcept
+{
+    return {1, 'p'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::nano) noexcept
+{
+    return {1, 'n'};
+}
+
+template <class CharT>
+constexpr
+inline
+typename std::enable_if
+<
+    std::is_same<CharT, char>::value,
+    std::string
+>::type
+msl(std::micro) noexcept
+{
+    return "\xC2\xB5";
+}
+
+template <class CharT>
+constexpr
+inline
+typename std::enable_if
+<
+    !std::is_same<CharT, char>::value,
+    std::basic_string<CharT>
+>::type
+msl(std::micro) noexcept
+{
+    return {1, CharT(static_cast<unsigned char>('\xB5'))};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::milli) noexcept
+{
+    return {1, 'm'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::centi) noexcept
+{
+    return {1, 'c'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::deci) noexcept
+{
+    return {1, 'd'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::deca) noexcept
+{
+    return {'d', 'a'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::hecto) noexcept
+{
+    return {1, 'h'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::kilo) noexcept
+{
+    return {1, 'k'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::mega) noexcept
+{
+    return {1, 'M'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::giga) noexcept
+{
+    return {1, 'G'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::tera) noexcept
+{
+    return {1, 'T'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::peta) noexcept
+{
+    return {1, 'P'};
+}
+
+template <class CharT>
+constexpr
+inline
+std::basic_string<CharT>
+msl(std::exa) noexcept
+{
+    return {1, 'E'};
+}
+
+template <class CharT, class Rep, class Period>
+std::basic_string<CharT>
+get_units(const std::chrono::duration<Rep, Period>&)
+{
+    return msl<CharT>(Period{}) + CharT{'s'};
+}
+
+template <class CharT, class Rep>
+std::basic_string<CharT>
+get_units(const std::chrono::duration<Rep, std::ratio<1>>&)
+{
+    return {1, 's'};
+}
+
+template <class CharT, class Rep>
+std::basic_string<CharT>
+get_units(const std::chrono::duration<Rep, std::ratio<60>>&)
+{
+    return {'m', 'i', 'n'};
+}
+
+template <class CharT, class Rep>
+std::basic_string<CharT>
+get_units(const std::chrono::duration<Rep, std::ratio<3600>>&)
+{
+    return {1, 'h'};
+}
+
+#endif  //  __cplusplus >= 201402
+
+}  // namespace detail
+
+template <class CharT, class Traits, class Rep, class Period>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os,
+           const std::chrono::duration<Rep, Period>& d)
+{
+    using namespace std::chrono;
+    return os << d.count()
+              << detail::get_units<CharT>(duration<Rep, typename Period::type>{});
+}
+
+}  // namespace date
+
+#endif  // CHRONO_IO_H