diff --git a/include/xlnt/cell/cell.hpp b/include/xlnt/cell/cell.hpp
index fc79ee13..658ab54d 100644
--- a/include/xlnt/cell/cell.hpp
+++ b/include/xlnt/cell/cell.hpp
@@ -340,6 +340,11 @@ public:
     /// </summary>
     calendar get_base_date() const;
 
+    /// <summary>
+    /// Return to_check after checking encoding, size, and illegal characters.
+    /// </summary>
+    std::string check_string(const std::string &to_check);
+
     // operators
     
     /// <summary>
diff --git a/include/xlnt/utils/exceptions.hpp b/include/xlnt/utils/exceptions.hpp
index cfb4c6f7..924c80f3 100644
--- a/include/xlnt/utils/exceptions.hpp
+++ b/include/xlnt/utils/exceptions.hpp
@@ -35,4 +35,5 @@
 #include <xlnt/utils/named_range_exception.hpp>
 #include <xlnt/utils/read_only_workbook_exception.hpp>
 #include <xlnt/utils/sheet_title_exception.hpp>
+#include <xlnt/utils/unicode_decode_error.hpp>
 #include <xlnt/utils/value_error.hpp>
diff --git a/include/xlnt/utils/timedelta.hpp b/include/xlnt/utils/timedelta.hpp
index 79462084..400c0dec 100644
--- a/include/xlnt/utils/timedelta.hpp
+++ b/include/xlnt/utils/timedelta.hpp
@@ -36,10 +36,9 @@ struct XLNT_CLASS timedelta
 {
     static timedelta from_number(long double number);
 
-    timedelta(int days_, int hours_, int minutes_ = 0, int seconds_ = 0, int microseconds_ = 0)
-        : days(days_), hours(hours_), minutes(minutes_), seconds(seconds_), microseconds(microseconds_)
-    {
-    }
+    timedelta();
+
+    timedelta(int days_, int hours_, int minutes_, int seconds_, int microseconds_);
 
     double to_number() const;
 
diff --git a/include/xlnt/utils/unicode_decode_error.hpp b/include/xlnt/utils/unicode_decode_error.hpp
new file mode 100644
index 00000000..c554a723
--- /dev/null
+++ b/include/xlnt/utils/unicode_decode_error.hpp
@@ -0,0 +1,44 @@
+// Copyright (c) 2014-2015 Thomas Fussell
+// Copyright (c) 2010-2015 openpyxl
+//
+// 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, WRISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE
+//
+// @license: http://www.opensource.org/licenses/mit-license.php
+// @author: see AUTHORS file
+#pragma once
+
+#include <cstdint>
+#include <stdexcept>
+
+#include <xlnt/xlnt_config.hpp>
+
+namespace xlnt {
+
+/// <summary>
+/// Error for string encoding not matching workbook encoding
+/// </summary>
+class XLNT_CLASS unicode_decode_error : public std::runtime_error
+{
+  public:
+    unicode_decode_error();
+    unicode_decode_error(char c);
+    unicode_decode_error(std::uint8_t b);
+};
+
+} // namespace xlnt
diff --git a/include/xlnt/workbook/workbook.hpp b/include/xlnt/workbook/workbook.hpp
index 81f561df..ca654fe8 100644
--- a/include/xlnt/workbook/workbook.hpp
+++ b/include/xlnt/workbook/workbook.hpp
@@ -116,6 +116,8 @@ class XLNT_CLASS workbook
 
     friend void swap(workbook &left, workbook &right);
 
+    encoding get_encoding() const;
+
     worksheet get_active_sheet();
 
     bool get_guess_types() const;
@@ -153,14 +155,8 @@ class XLNT_CLASS workbook
     iterator begin();
     iterator end();
 
-    const_iterator begin() const
-    {
-        return cbegin();
-    }
-    const_iterator end() const
-    {
-        return cend();
-    }
+    const_iterator begin() const;
+    const_iterator end() const;
 
     const_iterator cbegin() const;
     const_iterator cend() const;
diff --git a/source/cell/cell.cpp b/source/cell/cell.cpp
index b7790371..28ed03c2 100644
--- a/source/cell/cell.cpp
+++ b/source/cell/cell.cpp
@@ -6,7 +6,9 @@
 #include <xlnt/cell/comment.hpp>
 #include <xlnt/packaging/document_properties.hpp>
 #include <xlnt/packaging/relationship.hpp>
+#include <xlnt/serialization/encoding.hpp>
 #include <xlnt/styles/color.hpp>
+#include <xlnt/styles/style.hpp>
 #include <xlnt/utils/date.hpp>
 #include <xlnt/utils/datetime.hpp>
 #include <xlnt/utils/time.hpp>
@@ -32,6 +34,159 @@ const std::unordered_map<std::string, int> &cell::error_codes()
     return *codes;
 };
 
+std::string cell::check_string(const std::string &to_check)
+{
+    // so we can modify it
+    std::string s = to_check;
+
+    if (s.size() == 0)
+    {
+        return s;
+    }
+
+    auto wb_encoding = get_parent().get_parent().get_encoding();
+
+    //XXX: use utfcpp for this!
+    switch(wb_encoding)
+    {
+    case encoding::latin1: break; // all bytes are valid in latin1
+    case encoding::ascii:
+        for (char c : s)
+        {
+            if (c < 0)
+            {
+                throw xlnt::unicode_decode_error(c);
+            }
+        }
+        break;
+    case encoding::utf8:
+    {
+        std::vector<std::uint8_t> bytes;
+
+        for (char c : s)
+        {
+            auto byte = static_cast<std::uint8_t>(c);
+
+            if (byte < 128)
+            {
+                if(!bytes.empty())
+                {
+                    throw xlnt::unicode_decode_error(c);
+                }
+            }
+            else
+            {
+                if(!bytes.empty())
+                {
+                    if(byte >> 6 != 2)
+                    {
+                        throw xlnt::unicode_decode_error(c);
+                    }
+                }
+            }
+
+            bytes.push_back(byte);
+
+            auto first_byte = bytes[0];
+            auto num_bytes = 0;
+
+            if(first_byte < 128)
+            {
+                num_bytes = 1;
+            }
+            else if(first_byte >> 5 == 0b110)
+            {
+                num_bytes = 2;
+            }
+            else if(first_byte >> 4 == 0b1110)
+            {
+                num_bytes = 3;
+            }
+            else if(first_byte >> 3 == 0b11110)
+            {
+                num_bytes = 4;
+            }
+            else if(first_byte >> 2 == 0b111110)
+            {
+                num_bytes = 5;
+            }
+            else if(first_byte >> 1 == 0b1111110)
+            {
+                num_bytes = 6;
+            }
+
+            if(num_bytes > bytes.size())
+            {
+                throw xlnt::unicode_decode_error(c);
+            }
+
+            if(num_bytes == bytes.size())
+            {
+                bytes.clear();
+            }
+        }
+
+        // Check last code point
+        if(!bytes.empty())
+        {
+            auto first_byte = bytes[0];
+            auto num_bytes = 0;
+
+            if(first_byte < 128)
+            {
+                num_bytes = 1;
+            }
+            else if(first_byte >> 5 == 0b110)
+            {
+                num_bytes = 2;
+            }
+            else if(first_byte >> 4 == 0b1110)
+            {
+                num_bytes = 3;
+            }
+            else if(first_byte >> 3 == 0b11110)
+            {
+                num_bytes = 4;
+            }
+            else if(first_byte >> 2 == 0b111110)
+            {
+                num_bytes = 5;
+            }
+            else if(first_byte >> 1 == 0b1111110)
+            {
+                num_bytes = 6;
+            }
+
+            if(num_bytes > bytes.size())
+            {
+                throw xlnt::unicode_decode_error();
+            }
+        }
+
+        break;
+    }
+    default:
+        // other encodings not supported yet
+        break;
+    } // switch(wb_encoding)
+
+    // check encoding?
+    if (s.size() > 32767)
+    {
+        s = s.substr(0, 32767); // max string length in Excel
+    }
+
+    for (char c : s)
+    {
+        if (c >= 0 && (c <= 8 || c == 11 || c == 12 || (c >= 14 && c <= 31)))
+        {
+            throw xlnt::illegal_character_error(c);
+        }
+    }
+
+    return s;
+}
+
 cell::cell() : d_(nullptr)
 {
 }
@@ -169,7 +324,7 @@ XLNT_FUNCTION void cell::set_value(long double d)
 template <>
 XLNT_FUNCTION void cell::set_value(std::string s)
 {
-    d_->set_string(s, get_parent().get_parent().get_guess_types());
+    d_->set_string(check_string(s), get_parent().get_parent().get_guess_types());
 
 	if (get_data_type() == type::string && !s.empty())
 	{
@@ -497,7 +652,15 @@ const number_format &cell::get_number_format() const
 
 const font &cell::get_font() const
 {
-    return get_parent().get_parent().get_font(d_->style_id_);
+    if (d_->has_style_)
+    {
+        auto font_id = get_parent().get_parent().get_styles()[d_->style_id_].get_font_id();
+        return get_parent().get_parent().get_font(font_id);
+    }
+    else
+    {
+        return get_parent().get_parent().get_font(0);
+    }
 }
 
 const fill &cell::get_fill() const
@@ -642,6 +805,12 @@ XLNT_FUNCTION timedelta cell::get_value() const
     return timedelta::from_number(d_->value_numeric_);
 }
 
+void cell::set_font(const font &font_)
+{
+    d_->has_style_ = true;
+    d_->style_id_ = get_parent().get_parent().set_font(font_, d_->style_id_);
+}
+
 void cell::set_number_format(const number_format &number_format_)
 {
     d_->has_style_ = true;
diff --git a/source/cell/tests/test_cell.hpp b/source/cell/tests/test_cell.hpp
index 0dd0655b..a3f8977c 100644
--- a/source/cell/tests/test_cell.hpp
+++ b/source/cell/tests/test_cell.hpp
@@ -7,6 +7,7 @@
 #include <xlnt/cell/cell.hpp>
 #include <xlnt/cell/cell_reference.hpp>
 #include <xlnt/cell/comment.hpp>
+#include <xlnt/serialization/encoding.hpp>
 #include <xlnt/styles/alignment.hpp>
 #include <xlnt/styles/border.hpp>
 #include <xlnt/styles/font.hpp>
@@ -265,31 +266,14 @@ public:
         cell.set_value(std::string(1, 13));  // Carriage return
         cell.set_value(" Leading and trailing spaces are legal ");
     }
-    /*
-    values = (
-              ('30:33.865633336', [('', '', '', '30', '33', '865633')]),
-              ('03:40:16', [('03', '40', '16', '', '', '')]),
-              ('03:40', [('03', '40', '',  '', '', '')]),
-              ('55:72:12', []),
-              )
-    @pytest.mark.parametrize("value, expected",
-                             values)
-     */
-    void test_time_regex()
-    {
-        /*
-        from openpyxl.cell.cell import TIME_REGEX;
-        m = TIME_REGEX.findall(value);
-        TS_ASSERT(m == expected;
-         */
-    }
     
     void test_timedelta()
     {
         auto ws = wb.create_sheet();
         auto cell = ws.get_cell(xlnt::cell_reference(1, 1));
         
-        cell.set_value(xlnt::timedelta(1, 3));
+        cell.set_value(xlnt::timedelta(1, 3, 0, 0, 0));
+
         TS_ASSERT(cell.get_value<long double>() == 1.125);
         TS_ASSERT(cell.get_data_type() == xlnt::cell::type::numeric);
         TS_ASSERT(!cell.is_date());
@@ -352,43 +336,42 @@ public:
     
     void test_cell_offset()
     {
-        /*
         auto ws = wb.create_sheet();
         auto cell = ws.get_cell(xlnt::cell_reference(1, 1));
-        TS_ASSERT(cell.offset(2, 1).get_reference() == "B3");
-         */
+        TS_ASSERT(cell.offset(1, 2).get_reference() == "B3");
+    }
+
+    std::string make_latin1_string()
+    {
+        unsigned char pound = 163;
+        auto test_string = "Compound Value (" + std::string(1, pound) + ")";
+        return test_string;
     }
     
     void test_bad_encoding()
     {
-        /*
-        unsigned char pound = 163;
-        auto test_string = "Compount Value (" + std::string(pound) + ")";
         auto ws = wb.create_sheet();
-        cell = ws[xlnt::cell_reference("A1")];
-        TS_ASSERT_THROWS(cell.check_string(test_string), xlnt::unicode_decode_error);
-        TS_ASSERT_THROWS(cell.set_value(test_string), xlnt::unicode_decode_error);
-         */
+        auto cell = ws[xlnt::cell_reference("A1")];
+        TS_ASSERT_THROWS(cell.check_string(make_latin1_string()), xlnt::unicode_decode_error);
+        TS_ASSERT_THROWS(cell.set_value(make_latin1_string()), xlnt::unicode_decode_error);
     }
     
     void test_good_encoding()
     {
-        /*
-        auto wb = xlnt::workbook(xlnt::encoding::latin1);
-        auto ws = wb.get_active_sheet();
+        xlnt::workbook latin1_wb(xlnt::encoding::latin1);
+        auto ws = latin1_wb.get_active_sheet();
         auto cell = ws[xlnt::cell_reference("A1")];
-        cell.set_value(test_string);
-         */
+        cell.check_string(make_latin1_string());
+        cell.set_value(make_latin1_string());
     }
     
-    void _test_font()
+    void test_font()
     {
         xlnt::font font;
         font.set_bold(true);
-        auto ws = wb.create_sheet();
-        ws.get_parent().add_font(font);
-    
+        auto ws = wb.create_sheet();    
         auto cell = xlnt::cell(ws, "A1");
+        cell.set_font(font);
         TS_ASSERT_EQUALS(cell.get_font(), font);
     }
     
diff --git a/source/detail/cell_impl.cpp b/source/detail/cell_impl.cpp
index 7da4131a..ed60b3fe 100644
--- a/source/detail/cell_impl.cpp
+++ b/source/detail/cell_impl.cpp
@@ -56,5 +56,59 @@ cell_impl &cell_impl::operator=(const cell_impl &rhs)
     return *this;
 }
 
+cell cell_impl::self()
+{
+    return xlnt::cell(this);
+}
+
+void cell_impl::set_string(const std::string &s, bool guess_types)
+{
+    value_string_ = s;
+    type_ = cell::type::string;
+
+    if (value_string_.size() > 1 && value_string_.front() == '=')
+    {
+        formula_ = value_string_;
+        type_ = cell::type::formula;
+        value_string_.clear();
+    }
+    else if (cell::error_codes().find(s) != cell::error_codes().end())
+    {
+        type_ = cell::type::error;
+    }
+    else if (guess_types)
+    {
+        auto percentage = cast_percentage(s);
+
+        if (percentage.first)
+        {
+            value_numeric_ = percentage.second;
+            type_ = cell::type::numeric;
+            self().set_number_format(xlnt::number_format::percentage());
+        }
+        else
+        {
+            auto time = cast_time(s);
+
+            if (time.first)
+            {
+                type_ = cell::type::numeric;
+                self().set_number_format(number_format::date_time6());
+                value_numeric_ = time.second.to_number();
+            }
+            else
+            {
+                auto numeric = cast_numeric(s);
+
+                if (numeric.first)
+                {
+                    value_numeric_ = numeric.second;
+                    type_ = cell::type::numeric;
+                }
+            }
+        }
+    }
+}
+
 } // namespace detail
 } // namespace xlnt
diff --git a/source/detail/cell_impl.hpp b/source/detail/cell_impl.hpp
index 49beea12..bf5cb31d 100644
--- a/source/detail/cell_impl.hpp
+++ b/source/detail/cell_impl.hpp
@@ -14,32 +14,6 @@
 
 namespace {
 
-// return s after checking encoding, size, and illegal characters
-std::string check_string(std::string s)
-{
-    if (s.size() == 0)
-    {
-        return s;
-    }
-
-    // check encoding?
-
-    if (s.size() > 32767)
-    {
-        s = s.substr(0, 32767); // max string length in Excel
-    }
-
-    for (char c : s)
-    {
-        if (c >= 0 && (c <= 8 || c == 11 || c == 12 || (c >= 14 && c <= 31)))
-        {
-            throw xlnt::illegal_character_error(c);
-        }
-    }
-
-    return s;
-}
-
 std::pair<bool, long double> cast_numeric(const std::string &s)
 {
     const char *str = s.c_str();
@@ -124,59 +98,9 @@ struct cell_impl
     cell_impl(const cell_impl &rhs);
     cell_impl &operator=(const cell_impl &rhs);
 
-    cell self()
-    {
-        return xlnt::cell(this);
-    }
+    cell self();
 
-    void set_string(const std::string &s, bool guess_types)
-    {
-        value_string_ = check_string(s);
-        type_ = cell::type::string;
-
-        if (value_string_.size() > 1 && value_string_.front() == '=')
-        {
-            formula_ = value_string_;
-            type_ = cell::type::formula;
-            value_string_.clear();
-        }
-        else if (cell::error_codes().find(s) != cell::error_codes().end())
-        {
-            type_ = cell::type::error;
-        }
-        else if (guess_types)
-        {
-            auto percentage = cast_percentage(s);
-
-            if (percentage.first)
-            {
-                value_numeric_ = percentage.second;
-                type_ = cell::type::numeric;
-                self().set_number_format(xlnt::number_format::percentage());
-            }
-            else
-            {
-                auto time = cast_time(s);
-
-                if (time.first)
-                {
-                    type_ = cell::type::numeric;
-                    self().set_number_format(number_format::date_time6());
-                    value_numeric_ = time.second.to_number();
-                }
-                else
-                {
-                    auto numeric = cast_numeric(s);
-
-                    if (numeric.first)
-                    {
-                        value_numeric_ = numeric.second;
-                        type_ = cell::type::numeric;
-                    }
-                }
-            }
-        }
-    }
+    void set_string(const std::string &s, bool guess_types);
 
     cell::type type_;
 
diff --git a/source/detail/workbook_impl.hpp b/source/detail/workbook_impl.hpp
index 81e015f7..6cbf6816 100644
--- a/source/detail/workbook_impl.hpp
+++ b/source/detail/workbook_impl.hpp
@@ -83,6 +83,8 @@ struct workbook_impl
     manifest manifest_;
 
     theme theme_;
+
+    encoding encoding_;
 };
 
 } // namespace detail
diff --git a/source/serialization/tests/test_read.hpp b/source/serialization/tests/test_read.hpp
index 92238ec6..7fb21b29 100644
--- a/source/serialization/tests/test_read.hpp
+++ b/source/serialization/tests/test_read.hpp
@@ -299,8 +299,7 @@ public:
     {
         auto path = PathHelper::GetDataDirectory("/reader/formulae.xlsx");
         
-        
-        xlnt::workbook wb;
+        xlnt::workbook wb(xlnt::encoding::latin1);
         xlnt::excel_serializer serializer(wb);
         
         serializer.load_workbook(path, false, true);
diff --git a/source/utils/exceptions.cpp b/source/utils/exceptions.cpp
index 5045c86c..bb372b72 100644
--- a/source/utils/exceptions.cpp
+++ b/source/utils/exceptions.cpp
@@ -48,6 +48,16 @@ illegal_character_error::illegal_character_error(char c)
 {
 }
 
+unicode_decode_error::unicode_decode_error()
+    : std::runtime_error("unicode decode error")
+{
+}
+
+unicode_decode_error::unicode_decode_error(char)
+    : std::runtime_error("unicode decode error")
+{
+}
+
 value_error::value_error()
     : std::runtime_error("value error")
 {
diff --git a/source/utils/tests/test_timedelta.hpp b/source/utils/tests/test_timedelta.hpp
index 88858c75..5e6ca2f0 100644
--- a/source/utils/tests/test_timedelta.hpp
+++ b/source/utils/tests/test_timedelta.hpp
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <iostream>
 #include <cxxtest/TestSuite.h>
 
 class test_timedelta : public CxxTest::TestSuite
@@ -8,10 +9,25 @@ public:
     void test_from_number()
     {
         auto td = xlnt::timedelta::from_number(1.0);
+
         TS_ASSERT(td.days == 1);
         TS_ASSERT(td.hours == 0);
         TS_ASSERT(td.minutes == 0);
         TS_ASSERT(td.seconds == 0);
         TS_ASSERT(td.microseconds == 0);
     }
+
+    void test_round_trip()
+    {
+    	long double time = 3.14159265;
+        auto td = xlnt::timedelta::from_number(time);
+        auto time_rt = td.to_number();
+        TS_ASSERT_EQUALS(time, time_rt);
+    }
+
+    void test_to_number()
+    {
+    	xlnt::timedelta td(1, 1, 1, 1, 1);
+    	TS_ASSERT_EQUALS(td.to_number(), 1.0423726851999999);
+    }
 };
diff --git a/source/utils/timedelta.cpp b/source/utils/timedelta.cpp
index ddcc976a..edce0d9e 100644
--- a/source/utils/timedelta.cpp
+++ b/source/utils/timedelta.cpp
@@ -5,28 +5,72 @@
 
 namespace xlnt {
 
-double timedelta::to_number() const
+timedelta::timedelta() : timedelta(0, 0, 0, 0, 0)
 {
-    return days + hours / 24.0;
 }
 
-timedelta timedelta::from_number(long double number)
+timedelta::timedelta(int days_, int hours_, int minutes_, int seconds_, int microseconds_)
+        : days(days_), 
+          hours(hours_), 
+          minutes(minutes_), 
+          seconds(seconds_), 
+          microseconds(microseconds_)
+    {
+    }
+
+double timedelta::to_number() const
 {
-    int days = static_cast<int>(number);
-    number -= days;
-    number *= 24;
-    int hours = static_cast<int>(number);
-    number -= hours;
-    number *= 60;
-    int minutes = static_cast<int>(number);
-    number -= minutes;
-    number *= 60;
-    int seconds = static_cast<int>(number);
-    number -= seconds;
-    number *= 1000000;
-    int microseconds = static_cast<int>(number + 0.5);
+    std::uint64_t total_microseconds = static_cast<std::uint64_t>(microseconds);
+    total_microseconds += static_cast<std::uint64_t>(seconds * 1e6);
+    total_microseconds += static_cast<std::uint64_t>(minutes * 1e6 * 60);
+    auto microseconds_per_hour = static_cast<std::uint64_t>(1e6) * 60 * 60;
+    total_microseconds += static_cast<std::uint64_t>(hours) * microseconds_per_hour;
+    auto number = total_microseconds / (24.0L * microseconds_per_hour);
+    auto hundred_billion = static_cast<std::uint64_t>(1e9) * 100;
+    number = std::floor(number * hundred_billion + 0.5L) / hundred_billion;
+    number += days;
     
-    return timedelta(days, hours, minutes, seconds, microseconds);
+    return number;
+}
+
+timedelta timedelta::from_number(long double raw_time)
+{
+    timedelta result;
+
+    double integer_part;
+    double fractional_part = std::modf((double)raw_time, &integer_part);
+
+    result.days = integer_part;
+
+    fractional_part *= 24;
+    result.hours = (int)fractional_part;
+    fractional_part = 60 * (fractional_part - result.hours);
+    result.minutes = (int)fractional_part;
+    fractional_part = 60 * (fractional_part - result.minutes);
+    result.seconds = (int)fractional_part;
+    fractional_part = 1000000 * (fractional_part - result.seconds);
+    result.microseconds = (int)fractional_part;
+    
+    if (result.microseconds == 999999 && fractional_part - result.microseconds > 0.5)
+    {
+        result.microseconds = 0;
+        result.seconds += 1;
+        
+        if (result.seconds == 60)
+        {
+            result.seconds = 0;
+            result.minutes += 1;
+            
+            //TODO: too much nesting
+            if (result.minutes == 60)
+            {
+                result.minutes = 0;
+                result.hours += 1;
+            }
+        }
+    }
+    
+    return result;
 }
 
 } // namespace xlnt
diff --git a/source/workbook/workbook.cpp b/source/workbook/workbook.cpp
index 5a9c353f..6fa8998b 100644
--- a/source/workbook/workbook.cpp
+++ b/source/workbook/workbook.cpp
@@ -60,6 +60,11 @@ workbook::workbook() : d_(new detail::workbook_impl())
     d_->manifest_.add_override_type("/docProps/app.xml", "application/vnd.openxmlformats-officedocument.extended-properties+xml");
 }
 
+workbook::workbook(encoding e) : workbook()
+{
+    d_->encoding_ = e;
+}
+
 workbook::iterator::iterator(workbook &wb, std::size_t index) : wb_(wb), index_(index)
 {
 }
@@ -423,6 +428,11 @@ worksheet workbook::create_sheet(const std::string &title)
     return ws;
 }
 
+encoding workbook::get_encoding() const
+{
+    return d_->encoding_;
+}
+
 workbook::iterator workbook::begin()
 {
     return iterator(*this, 0);
@@ -433,6 +443,16 @@ workbook::iterator workbook::end()
     return iterator(*this, d_->worksheets_.size());
 }
 
+workbook::const_iterator workbook::begin() const
+{
+    return cbegin();
+}
+
+workbook::const_iterator workbook::end() const
+{
+    return cend();
+}
+
 workbook::const_iterator workbook::cbegin() const
 {
     return const_iterator(*this, 0);
@@ -681,39 +701,78 @@ const font &workbook::get_font(std::size_t font_id) const
 std::size_t workbook::set_font(const font &font_, std::size_t style_id)
 {
     auto match = std::find(d_->fonts_.begin(), d_->fonts_.end(), font_);
-    std::size_t font_index = 0;
+    std::size_t font_id = 0;
 
     if (match == d_->fonts_.end())
     {
         d_->fonts_.push_back(font_);
-        font_index = d_->fonts_.size() - 1;
+        font_id = d_->fonts_.size() - 1;
     }
     else
     {
-        font_index = static_cast<std::size_t>(match - d_->fonts_.begin());
+        font_id = match - d_->fonts_.begin();
     }
 
-    auto existing_style = d_->styles_[style_id];
+    if (d_->styles_.empty())
+    {
+        style new_style;
 
-    if (font_index == existing_style.font_id_)
+        new_style.id_ = 0;
+        new_style.border_id_ = 0;
+        new_style.fill_id_ = 0;
+        new_style.font_id_ = font_id;
+        new_style.font_apply_ = true;
+        new_style.number_format_id_ = 0;
+
+        if (d_->borders_.empty())
+        {
+            d_->borders_.push_back(new_style.get_border());
+        }
+
+        if (d_->fills_.empty())
+        {
+            d_->fills_.push_back(new_style.get_fill());
+        }
+
+        if (d_->number_formats_.empty())
+        {
+            d_->number_formats_.push_back(new_style.get_number_format());
+        }
+
+        d_->styles_.push_back(new_style);
+
+        return 0;
+    }
+
+    // If the style is unchanged, just return it.
+    auto &existing_style = d_->styles_[style_id];
+    existing_style.font_apply_ = true;
+
+    if (font_id == existing_style.font_id_)
     {
         // no change
         return style_id;
     }
 
+    // Make a new style with this format.
     auto new_style = existing_style;
-    new_style.font_id_ = font_index;
 
+    new_style.font_id_ = font_id;
+    new_style.font_ = font_;
+
+    // Check if the new style is already applied to a different cell. If so, reuse it.
     auto style_match = std::find(d_->styles_.begin(), d_->styles_.end(), new_style);
 
     if (style_match != d_->styles_.end())
     {
-        return static_cast<std::size_t>(style_match - d_->styles_.begin());
+        return style_match->get_id();
     }
 
+    // No match found, so add it.
+    new_style.id_ = d_->styles_.size();
     d_->styles_.push_back(new_style);
 
-    return d_->styles_.size() - 1;
+    return new_style.id_;
 }
 
 const fill &workbook::get_fill(std::size_t fill_id) const
@@ -766,6 +825,7 @@ bool workbook::get_quote_prefix(std::size_t style_id) const
     return d_->styles_[style_id].quote_prefix_;
 }
 
+//TODO: this is terrible!
 std::size_t workbook::set_number_format(const xlnt::number_format &format, std::size_t style_id)
 {
     auto match = std::find(d_->number_formats_.begin(), d_->number_formats_.end(), format);