diff --git a/include/xlnt/cell/cell.hpp b/include/xlnt/cell/cell.hpp
index ebe37f8d..18161adb 100644
--- a/include/xlnt/cell/cell.hpp
+++ b/include/xlnt/cell/cell.hpp
@@ -139,7 +139,7 @@ public:
     cell &operator=(const time &value);
     cell &operator=(const datetime &value);
     
-    bool operator==(const cell &comparand) const { return d_ == comparand.d_; }
+    bool operator==(const cell &comparand) const;
     bool operator==(std::nullptr_t) const;
     bool operator==(bool comparand) const;
     bool operator==(int comparand) const;
diff --git a/include/xlnt/common/datetime.hpp b/include/xlnt/common/datetime.hpp
index 9c866fe0..41b0943c 100644
--- a/include/xlnt/common/datetime.hpp
+++ b/include/xlnt/common/datetime.hpp
@@ -29,14 +29,14 @@ namespace xlnt {
 struct date
 {
     static date today();
-    static date from_number(long double number, int base_year = 1900);
+    static date from_number(int days_since_base_year, int base_year = 1900);
 
     date(int year, int month, int day)
         : year(year), month(month), day(day)
     {
     }
 
-    double to_number(int base_year = 1900) const;
+    int to_number(int base_year = 1900) const;
     bool operator==(const date &comparand) const;
 
     int year;
@@ -47,7 +47,7 @@ struct date
 struct time
 {
     static time now();
-    static time from_number(long double number, int base_year = 1900);
+    static time from_number(long double number);
 
     time(int hour = 0, int minute = 0, int second = 0, int microsecond = 0)
         : hour(hour), minute(minute), second(second), microsecond(microsecond)
@@ -55,7 +55,7 @@ struct time
     }
     explicit time(const std::string &time_string);
 
-    double to_number(int base_year = 1900) const;
+    double to_number() const;
     bool operator==(const time &comparand) const;
 
     int hour;
diff --git a/include/xlnt/workbook/workbook.hpp b/include/xlnt/workbook/workbook.hpp
index 79a6f992..91987eb8 100644
--- a/include/xlnt/workbook/workbook.hpp
+++ b/include/xlnt/workbook/workbook.hpp
@@ -23,6 +23,7 @@
 // @author: see AUTHORS file
 #pragma once
 
+#include <memory>
 #include <string>
 #include <unordered_map>
 #include <utility>
@@ -161,7 +162,7 @@ public:
 private:
     friend class worksheet;
     bool get_already_saved() const;
-    detail::workbook_impl *d_;
+    std::unique_ptr<detail::workbook_impl> d_;
 };
     
 } // namespace xlnt
diff --git a/source/cell.cpp b/source/cell.cpp
index 0bae518a..e62d0cbb 100644
--- a/source/cell.cpp
+++ b/source/cell.cpp
@@ -287,8 +287,7 @@ bool cell::operator==(const time &comparand) const
         return false;
     }
     
-    auto base_year = worksheet(d_->parent_).get_parent().get_base_year();
-    return time::from_number(d_->numeric_value, base_year) == comparand;
+    return time::from_number(d_->numeric_value) == comparand;
 }
 
 bool cell::operator==(const date &comparand) const
@@ -299,7 +298,7 @@ bool cell::operator==(const date &comparand) const
     }
     
     auto base_year = worksheet(d_->parent_).get_parent().get_base_year();
-    return date::from_number(d_->numeric_value, base_year) == comparand;
+    return date::from_number((int)d_->numeric_value, base_year) == comparand;
 }
 
 bool cell::operator==(const datetime &comparand) const
@@ -313,6 +312,43 @@ bool cell::operator==(const datetime &comparand) const
     return datetime::from_number(d_->numeric_value, base_year) == comparand;
 }
 
+bool cell::operator==(const cell &comparand) const
+{
+    if(comparand == nullptr)
+    {
+        return d_ == nullptr;
+    }
+
+    if(comparand.get_data_type() != get_data_type())
+    {
+        return false;
+    }
+
+    switch(get_data_type())
+    {
+    case type::boolean:
+        return d_->numeric_value == comparand.d_->numeric_value;
+    case type::error:
+        return d_->string_value == comparand.d_->string_value;
+    case type::string:
+        return d_->string_value == comparand.d_->string_value;
+    case type::formula:
+        return d_->string_value == comparand.d_->string_value;
+    case type::null:
+        return true;
+    case type::numeric:
+        if(is_date() && comparand.is_date())
+        {
+            auto base_year = worksheet(d_->parent_).get_parent().get_base_year();
+            auto other_base_year = worksheet(comparand.d_->parent_).get_parent().get_base_year();
+            return date::from_number((int)d_->numeric_value, base_year) == date::from_number((int)comparand.d_->numeric_value, other_base_year);
+        }
+        return d_->numeric_value == comparand.d_->numeric_value;
+    }
+
+    return false;
+}
+
 bool operator==(int comparand, const xlnt::cell &cell)
 {
     return cell == comparand;
@@ -481,7 +517,8 @@ cell &cell::operator=(const time &value)
 cell &cell::operator=(const date &value)
 {
     d_->type_ = type::numeric;
-    d_->numeric_value = value.to_number();
+    auto base_year = worksheet(d_->parent_).get_parent().get_base_year();
+    d_->numeric_value = value.to_number(base_year);
     d_->is_date_ = true;
     return *this;
 }
@@ -489,7 +526,8 @@ cell &cell::operator=(const date &value)
 cell &cell::operator=(const datetime &value)
 {
     d_->type_ = type::numeric;
-    d_->numeric_value = value.to_number();
+    auto base_year = worksheet(d_->parent_).get_parent().get_base_year();
+    d_->numeric_value = value.to_number(base_year);
     d_->is_date_ = true;
     return *this;
 }
diff --git a/source/datetime.cpp b/source/datetime.cpp
index c9856437..536bae3a 100644
--- a/source/datetime.cpp
+++ b/source/datetime.cpp
@@ -5,7 +5,7 @@
 
 namespace xlnt {
 
-time time::from_number(long double raw_time, int base_year)
+time time::from_number(long double raw_time)
 {
     double integer_part;
     double fractional_part = std::modf((double)raw_time, &integer_part);
@@ -35,49 +35,45 @@ time time::from_number(long double raw_time, int base_year)
     return time(hour, minute, second, microsecond);
 }
 
-date date::from_number(long double number, int base_year)
+date date::from_number(int days_since_base_year, int base_year)
 {
-    int year = (int)number / 365;
-    number -= year * 365;
-    int month = (int)number / 30;
-    number -= month * 30;
-    int day = (int)number;
-    return date(year + base_year, month, day + 1);
+    date result(0, 0, 0);
+
+    if(base_year == 1904)
+    {
+        days_since_base_year += 1462;
+    }
+
+    if(days_since_base_year == 60)
+    {
+        result.day = 29;
+        result.month = 2;
+        result.year = 1900;
+    }
+    else if(days_since_base_year < 60)
+    {
+        days_since_base_year++;
+    }
+
+    int l = days_since_base_year + 68569 + 2415019;
+    int n = int((4 * l) / 146097);
+    l = l - int((146097 * n + 3) / 4);
+    int i = int((4000 * (l + 1)) / 1461001);
+    l = l - int((1461 * i) / 4) + 31;
+    int j = int((80 * l) / 2447);
+    result.day = l - int((2447 * j) / 80);
+    l = int(j / 11);
+    result.month = j + 2 - (12 * l);
+    result.year = 100 * (n - 49) + i + l;
+
+    return result;
 }
 
 datetime datetime::from_number(long double raw_time, int base_year)
 {
-    double integer_part;
-    double fractional_part = std::modf((double)raw_time, &integer_part);
-    fractional_part *= 24;
-    int hour = (int)fractional_part;
-    fractional_part = 60 * (fractional_part - hour);
-    int minute = (int)fractional_part;
-    fractional_part = 60 * (fractional_part - minute);
-    int second = (int)fractional_part;
-    fractional_part = 1000000 * (fractional_part - second);
-    int microsecond = (int)fractional_part;
-    if(microsecond == 999999 && fractional_part - microsecond > 0.5)
-    {
-        microsecond = 0;
-        second += 1;
-        if(second == 60)
-        {
-            second = 0;
-            minute += 1;
-            if(minute == 60)
-            {
-                minute = 0;
-                hour += 1;
-            }
-        }
-    }
-    int year = (int)integer_part / 365;
-    integer_part -= year * 365;
-    int month = (int)integer_part / 30;
-    integer_part -= month * 30;
-    int day = (int)integer_part;
-    return datetime(year + base_year, month, day + 1, hour, minute, second, microsecond);
+    auto date_part = date::from_number((int)raw_time, base_year);
+    auto time_part = time::from_number(raw_time);
+    return datetime(date_part.year, date_part.month, date_part.day, time_part.hour, time_part.minute, time_part.second, time_part.microsecond);
 }
 
 bool date::operator==(const date &comparand) const
@@ -122,7 +118,7 @@ time::time(const std::string &time_string) : hour(0), minute(0), second(0), micr
     }
 }
 
-double time::to_number(int base_year) const
+double time::to_number() const
 {
     double number = microsecond;
     number /= 1000000;
@@ -135,38 +131,49 @@ double time::to_number(int base_year) const
     return number;
 }
 
-double date::to_number(int base_year) const
+int date::to_number(int base_year) const
 {
-    double number = (day - 1) + month * 30 + (year - base_year) * 365;
-    return number;
+    if(day == 29 && month == 2 && year == 1900)
+    {
+        return 60;
+    }
+
+    int days_since_1900 = int((1461 * (year + 4800 + int((month - 14) / 12))) / 4)
+        + int((367 * (month - 2 - 12 * ((month - 14) / 12))) / 12)
+        - int((3 * (int((year + 4900 + int((month - 14) / 12)) / 100))) / 4)
+        + day - 2415019 - 32075;
+
+    if(days_since_1900 <= 60)
+    {
+        days_since_1900--;
+    }
+
+    if(base_year == 1904)
+    {
+        return days_since_1900 - 1461;
+    }
+
+    return days_since_1900;
 }
 
 double datetime::to_number(int base_year) const
 {
-    double number = microsecond;
-    number /= 1000000;
-    number += second;
-    number /= 60;
-    number += minute;
-    number /= 60;
-    number += hour;
-    number /= 24;
-    number += (day - 1) + month * 30 + (year - base_year) * 365;
-    return number;
+    return date(year, month, day).to_number(base_year) 
+        + time(hour, minute, second, microsecond).to_number();
 }
 
 date date::today()
 {
     std::time_t raw_time = std::time(0);
     std::tm now = *std::localtime(&raw_time);
-    return date(now.tm_year, now.tm_mon + 1, now.tm_mday);
+    return date(1900 + now.tm_year, now.tm_mon + 1, now.tm_mday);
 }
 
 datetime datetime::now()
 {
     std::time_t raw_time = std::time(0);
     std::tm now = *std::localtime(&raw_time);
-    return datetime(now.tm_year, now.tm_mon + 1, now.tm_mday, now.tm_hour, now.tm_min, now.tm_sec);
+    return datetime(1900 + now.tm_year, now.tm_mon + 1, now.tm_mday, now.tm_hour, now.tm_min, now.tm_sec);
 }
 
 } // namespace xlnt
diff --git a/source/detail/workbook_impl.hpp b/source/detail/workbook_impl.hpp
index 3759f15e..16035a2c 100644
--- a/source/detail/workbook_impl.hpp
+++ b/source/detail/workbook_impl.hpp
@@ -8,6 +8,8 @@ namespace detail {
 struct workbook_impl
 {
     workbook_impl(optimization o);
+    workbook_impl &operator=(const workbook_impl &) = delete;
+    workbook_impl(const workbook_impl &) = delete;
     bool already_saved_;
     bool optimized_read_;
     bool optimized_write_;
diff --git a/source/detail/worksheet_impl.hpp b/source/detail/worksheet_impl.hpp
index db16b455..2d76464e 100644
--- a/source/detail/worksheet_impl.hpp
+++ b/source/detail/worksheet_impl.hpp
@@ -34,6 +34,13 @@ struct worksheet_impl
         title_ = other.title_;
         freeze_panes_ = other.freeze_panes_;
         cell_map_ = other.cell_map_;
+        for(auto &row : cell_map_)
+        {
+            for(auto &cell : row.second)
+            {
+                cell.second.parent_ = this;
+            }
+        }
         relationships_ = other.relationships_;
         page_setup_ = other.page_setup_;
         auto_filter_ = other.auto_filter_;
diff --git a/source/workbook.cpp b/source/workbook.cpp
index df91308b..c8cb603a 100644
--- a/source/workbook.cpp
+++ b/source/workbook.cpp
@@ -188,10 +188,8 @@ worksheet workbook::create_sheet()
         title = "Sheet" + std::to_string(++index);
     }
 
-    d_->worksheets_.emplace_back(this, title);
-    worksheet ws(&d_->worksheets_.back());
-    
-    return ws;
+    d_->worksheets_.push_back(detail::worksheet_impl(this, title));
+    return worksheet(&d_->worksheets_.back());
 }
 
 void workbook::add_sheet(xlnt::worksheet worksheet)
@@ -551,7 +549,7 @@ bool workbook::save(const std::string &filename)
     
 bool workbook::operator==(const workbook &rhs) const
 {
-    return d_ == rhs.d_;
+    return d_.get() == rhs.d_.get();
 }
     
 }
diff --git a/tests/runner-autogen.cpp b/tests/runner-autogen.cpp
index 42daaaa2..6ea03b74 100644
--- a/tests/runner-autogen.cpp
+++ b/tests/runner-autogen.cpp
@@ -21,7 +21,7 @@ int main( int argc, char *argv[] ) {
     return status;
 }
 bool suite_test_cell_init = false;
-#include "/Users/thomas/Development/xlnt/tests/test_cell.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_cell.hpp"
 
 static test_cell suite_test_cell;
 
@@ -238,7 +238,7 @@ public:
  void runTest() { suite_test_cell.test_is_not_date_color_format(); }
 } testDescription_suite_test_cell_test_is_not_date_color_format;
 
-#include "/Users/thomas/Development/xlnt/tests/test_chart.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_chart.hpp"
 
 static test_chart suite_test_chart;
 
@@ -329,7 +329,7 @@ public:
  void runTest() { suite_test_chart.test_write_chart_scatter(); }
 } testDescription_suite_test_chart_test_write_chart_scatter;
 
-#include "/Users/thomas/Development/xlnt/tests/test_dump.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_dump.hpp"
 
 static test_dump suite_test_dump;
 
@@ -366,7 +366,7 @@ public:
  void runTest() { suite_test_dump.test_append_after_save(); }
 } testDescription_suite_test_dump_test_append_after_save;
 
-#include "/Users/thomas/Development/xlnt/tests/test_named_range.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_named_range.hpp"
 
 static test_named_range suite_test_named_range;
 
@@ -457,7 +457,7 @@ public:
  void runTest() { suite_test_named_range.test_can_be_saved(); }
 } testDescription_suite_test_named_range_test_can_be_saved;
 
-#include "/Users/thomas/Development/xlnt/tests/test_number_format.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_number_format.hpp"
 
 static test_number_format suite_test_number_format;
 
@@ -560,7 +560,7 @@ public:
  void runTest() { suite_test_number_format.test_mac_date(); }
 } testDescription_suite_test_number_format_test_mac_date;
 
-#include "/Users/thomas/Development/xlnt/tests/test_props.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_props.hpp"
 
 static test_props suite_test_props;
 
@@ -603,7 +603,7 @@ public:
  void runTest() { suite_test_props.test_write_properties_app(); }
 } testDescription_suite_test_props_test_write_properties_app;
 
-#include "/Users/thomas/Development/xlnt/tests/test_read.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_read.hpp"
 
 static test_read suite_test_read;
 
@@ -736,7 +736,7 @@ public:
  void runTest() { suite_test_read.test_read_date_value(); }
 } testDescription_suite_test_read_test_read_date_value;
 
-#include "/Users/thomas/Development/xlnt/tests/test_strings.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_strings.hpp"
 
 static test_strings suite_test_strings;
 
@@ -767,7 +767,7 @@ public:
  void runTest() { suite_test_strings.test_formatted_string_table(); }
 } testDescription_suite_test_strings_test_formatted_string_table;
 
-#include "/Users/thomas/Development/xlnt/tests/test_style.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_style.hpp"
 
 static test_style suite_test_style;
 
@@ -864,7 +864,7 @@ public:
  void runTest() { suite_test_style.test_read_cell_style(); }
 } testDescription_suite_test_style_test_read_cell_style;
 
-#include "/Users/thomas/Development/xlnt/tests/test_theme.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_theme.hpp"
 
 static test_theme suite_test_theme;
 
@@ -877,7 +877,7 @@ public:
  void runTest() { suite_test_theme.test_write_theme(); }
 } testDescription_suite_test_theme_test_write_theme;
 
-#include "/Users/thomas/Development/xlnt/tests/test_workbook.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_workbook.hpp"
 
 static test_workbook suite_test_workbook;
 
@@ -1004,7 +1004,7 @@ public:
  void runTest() { suite_test_workbook.test_write_regular_float(); }
 } testDescription_suite_test_workbook_test_write_regular_float;
 
-#include "/Users/thomas/Development/xlnt/tests/test_worksheet.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_worksheet.hpp"
 
 static test_worksheet suite_test_worksheet;
 
@@ -1173,7 +1173,7 @@ public:
  void runTest() { suite_test_worksheet.test_printer_settings(); }
 } testDescription_suite_test_worksheet_test_printer_settings;
 
-#include "/Users/thomas/Development/xlnt/tests/test_write.hpp"
+#include "C:\Users\taf656\Development\xlnt\tests\test_write.hpp"
 
 static test_write suite_test_write;
 
diff --git a/tests/test_dump.hpp b/tests/test_dump.hpp
index 0226256a..f936f756 100644
--- a/tests/test_dump.hpp
+++ b/tests/test_dump.hpp
@@ -57,7 +57,7 @@ public:
             std::vector<xlnt::date> current_row;
             for(std::size_t x = 0; x < letters.size(); x++)
             {
-                current_row.push_back(xlnt::date(2010 + x, 5, row + 1));
+                current_row.push_back(xlnt::date(2010 + (int)x, 5, row + 1));
             }
             ws.append(current_row);
         }
diff --git a/tests/test_read.hpp b/tests/test_read.hpp
index 11082527..ee5e55a7 100644
--- a/tests/test_read.hpp
+++ b/tests/test_read.hpp
@@ -160,7 +160,6 @@ public:
 
     void test_read_date_value()
     {
-        TS_SKIP("something bad is happening here...");
         //auto path = PathHelper::GetDataDirectory() + "/genuine/empty-with-styles.xlsx";
         //wb_with_styles.load(path);
         //worksheet_with_styles = wb_with_styles.get_sheet_by_name("Sheet1");