diff --git a/src/PhpSpreadsheet/Calculation.php b/src/PhpSpreadsheet/Calculation.php
index b755667a..17739346 100644
--- a/src/PhpSpreadsheet/Calculation.php
+++ b/src/PhpSpreadsheet/Calculation.php
@@ -2037,14 +2037,6 @@ class Calculation
         return self::$instance;
     }
 
-    /**
-     * Unset an instance of this class.
-     */
-    public function __destruct()
-    {
-        $this->workbook = null;
-    }
-
     /**
      * Flush the calculation cache for any existing instance of this class
      *        but only if a Calculation instance exists.
diff --git a/src/PhpSpreadsheet/Calculation/Financial.php b/src/PhpSpreadsheet/Calculation/Financial.php
index 27fcd616..919eb9e1 100644
--- a/src/PhpSpreadsheet/Calculation/Financial.php
+++ b/src/PhpSpreadsheet/Calculation/Financial.php
@@ -19,7 +19,7 @@ class Financial
      *
      * @return bool
      */
-    private static function isLastDayOfMonth($testDate)
+    private static function isLastDayOfMonth(\DateTime $testDate)
     {
         return $testDate->format('d') == $testDate->format('t');
     }
diff --git a/src/PhpSpreadsheet/Calculation/Statistical.php b/src/PhpSpreadsheet/Calculation/Statistical.php
index 9e0fe1cb..d49e71eb 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical.php
@@ -300,7 +300,7 @@ class Statistical
         $y = $x;
         if ($y > 0.0 && $y <= self::LOG_GAMMA_X_MAX_VALUE) {
             if ($y <= self::EPS) {
-                $res = -log(y);
+                $res = -log($y);
             } elseif ($y <= 1.5) {
                 // ---------------------
                 //    EPS .LT. X .LE. 1.5
diff --git a/src/PhpSpreadsheet/Helper/Html.php b/src/PhpSpreadsheet/Helper/Html.php
index 528833c3..457b4be8 100644
--- a/src/PhpSpreadsheet/Helper/Html.php
+++ b/src/PhpSpreadsheet/Helper/Html.php
@@ -581,6 +581,9 @@ class Html
 
     protected $stringData = '';
 
+    /**
+     * @var RichText
+     */
     protected $richTextObject;
 
     protected function initialise()
diff --git a/src/PhpSpreadsheet/Reader/DefaultReadFilter.php b/src/PhpSpreadsheet/Reader/DefaultReadFilter.php
index 347ff39c..e104186a 100644
--- a/src/PhpSpreadsheet/Reader/DefaultReadFilter.php
+++ b/src/PhpSpreadsheet/Reader/DefaultReadFilter.php
@@ -7,9 +7,9 @@ class DefaultReadFilter implements IReadFilter
     /**
      * Should this cell be read?
      *
-     * @param $column Column address (as a string value like "A", or "IV")
-     * @param $row Row number
-     * @param $worksheetName Optional worksheet name
+     * @param string $column Column address (as a string value like "A", or "IV")
+     * @param int $row Row number
+     * @param string $worksheetName Optional worksheet name
      *
      * @return bool
      */
diff --git a/src/PhpSpreadsheet/Reader/Html.php b/src/PhpSpreadsheet/Reader/Html.php
index d1e05ade..a38bb3b7 100644
--- a/src/PhpSpreadsheet/Reader/Html.php
+++ b/src/PhpSpreadsheet/Reader/Html.php
@@ -238,7 +238,7 @@ class Html extends BaseReader implements IReader
         return array_pop($this->nestedColumn);
     }
 
-    protected function flushCell($sheet, $column, $row, &$cellContent)
+    protected function flushCell(Worksheet $sheet, $column, $row, &$cellContent)
     {
         if (is_string($cellContent)) {
             //    Simple String content
diff --git a/src/PhpSpreadsheet/Reader/Slk.php b/src/PhpSpreadsheet/Reader/Slk.php
index aa94d739..ea69d29f 100644
--- a/src/PhpSpreadsheet/Reader/Slk.php
+++ b/src/PhpSpreadsheet/Reader/Slk.php
@@ -485,7 +485,7 @@ class Slk extends BaseReader implements IReader
      *
      * @param int $pValue Sheet index
      *
-     * @return SYLK
+     * @return Slk
      */
     public function setSheetIndex($pValue)
     {
diff --git a/src/PhpSpreadsheet/Reader/Xls.php b/src/PhpSpreadsheet/Reader/Xls.php
index fbb248da..d876e22d 100644
--- a/src/PhpSpreadsheet/Reader/Xls.php
+++ b/src/PhpSpreadsheet/Reader/Xls.php
@@ -23,7 +23,6 @@ use PhpOffice\PhpSpreadsheet\Style\Font;
 use PhpOffice\PhpSpreadsheet\Style\NumberFormat;
 use PhpOffice\PhpSpreadsheet\Style\Protection;
 use PhpOffice\PhpSpreadsheet\Worksheet;
-use PhpOffice\PhpSpreadsheet\Worksheet\Drawing;
 use PhpOffice\PhpSpreadsheet\Worksheet\MemoryDrawing;
 use PhpOffice\PhpSpreadsheet\Worksheet\PageSetup;
 use PhpOffice\PhpSpreadsheet\Worksheet\SheetView;
diff --git a/src/PhpSpreadsheet/Shared/JAMA/EigenvalueDecomposition.php b/src/PhpSpreadsheet/Shared/JAMA/EigenvalueDecomposition.php
index 3e59bddd..e72604f4 100644
--- a/src/PhpSpreadsheet/Shared/JAMA/EigenvalueDecomposition.php
+++ b/src/PhpSpreadsheet/Shared/JAMA/EigenvalueDecomposition.php
@@ -83,7 +83,7 @@ class EigenvalueDecomposition
             $i_ = $i - 1;
             // Scale to avoid under/overflow.
             $h = $scale = 0.0;
-            $scale += array_sum(array_map(abs, $this->d));
+            $scale += array_sum(array_map('abs', $this->d));
             if ($scale == 0.0) {
                 $this->e[$i] = $this->d[$i_];
                 $this->d = array_slice($this->V[$i_], 0, $i_);
diff --git a/src/PhpSpreadsheet/Shared/OLE.php b/src/PhpSpreadsheet/Shared/OLE.php
index bcec3df7..2f24ba8f 100644
--- a/src/PhpSpreadsheet/Shared/OLE.php
+++ b/src/PhpSpreadsheet/Shared/OLE.php
@@ -541,7 +541,7 @@ class OLE
     public static function OLE2LocalDate($string)
     {
         if (strlen($string) != 8) {
-            return new PEAR_Error('Expecting 8 byte string');
+            throw new ReaderException('Expecting 8 byte string');
         }
 
         // factor used for separating numbers into 4 bytes parts
diff --git a/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php b/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php
index 844a1dbb..a7649d29 100644
--- a/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php
+++ b/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php
@@ -47,7 +47,7 @@ class Root extends PPS
      */
     public function __construct($time_1st, $time_2nd, $raChild)
     {
-        $this->_tempDir = \PhpOffice\PhpSpreadsheet\Shared\File::sysGetTempDir();
+        $this->tempDirectory = \PhpOffice\PhpSpreadsheet\Shared\File::sysGetTempDir();
 
         parent::__construct(null, OLE::ascToUcs('Root Entry'), OLE::OLE_PPS_TYPE_ROOT, null, null, null, $time_1st, $time_2nd, null, $raChild);
     }
diff --git a/src/PhpSpreadsheet/Shared/Trend/ExponentialBestFit.php b/src/PhpSpreadsheet/Shared/Trend/ExponentialBestFit.php
index 87d4fa5a..05693b3c 100644
--- a/src/PhpSpreadsheet/Shared/Trend/ExponentialBestFit.php
+++ b/src/PhpSpreadsheet/Shared/Trend/ExponentialBestFit.php
@@ -61,10 +61,10 @@ class ExponentialBestFit extends BestFit
     public function getSlope($dp = 0)
     {
         if ($dp != 0) {
-            return round(exp($this->_slope), $dp);
+            return round(exp($this->slope), $dp);
         }
 
-        return exp($this->_slope);
+        return exp($this->slope);
     }
 
     /**
diff --git a/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php b/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php
index cfac30b4..3004930c 100644
--- a/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php
+++ b/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php
@@ -101,14 +101,14 @@ class PolynomialBestFit extends BestFit
     {
         if ($dp != 0) {
             $coefficients = [];
-            foreach ($this->_slope as $coefficient) {
+            foreach ($this->slope as $coefficient) {
                 $coefficients[] = round($coefficient, $dp);
             }
 
             return $coefficients;
         }
 
-        return $this->_slope;
+        return $this->slope;
     }
 
     public function getCoefficients($dp = 0)
@@ -164,7 +164,7 @@ class PolynomialBestFit extends BestFit
         }
 
         $this->intersect = array_shift($coefficients);
-        $this->_slope = $coefficients;
+        $this->slope = $coefficients;
 
         $this->calculateGoodnessOfFit($x_sum, $y_sum, $xx_sum, $yy_sum, $xy_sum);
         foreach ($this->xValues as $xKey => $xValue) {
@@ -188,10 +188,10 @@ class PolynomialBestFit extends BestFit
                 $this->order = $order;
                 $this->polynomialRegression($order, $yValues, $xValues);
                 if (($this->getGoodnessOfFit() < 0.0) || ($this->getGoodnessOfFit() > 1.0)) {
-                    $this->_error = true;
+                    $this->error = true;
                 }
             } else {
-                $this->_error = true;
+                $this->error = true;
             }
         }
     }
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php b/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
index 7b7ba007..eeb5ca90 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
@@ -6,6 +6,7 @@ use PhpOffice\PhpSpreadsheet\Cell;
 use PhpOffice\PhpSpreadsheet\RichText;
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
 use PhpOffice\PhpSpreadsheet\Shared\XMLWriter;
+use PhpOffice\PhpSpreadsheet\Worksheet;
 use PhpOffice\PhpSpreadsheet\Writer\Exception as WriterException;
 
 class StringTable extends WriterPart
@@ -20,45 +21,41 @@ class StringTable extends WriterPart
      *
      * @return string[] String table for worksheet
      */
-    public function createStringTable($pSheet = null, $pExistingTable = null)
+    public function createStringTable(Worksheet $pSheet, $pExistingTable = null)
     {
-        if ($pSheet !== null) {
-            // Create string lookup table
-            $aStringTable = [];
-            $cellCollection = null;
-            $aFlippedStringTable = null; // For faster lookup
+        // Create string lookup table
+        $aStringTable = [];
+        $cellCollection = null;
+        $aFlippedStringTable = null; // For faster lookup
 
-            // Is an existing table given?
-            if (($pExistingTable !== null) && is_array($pExistingTable)) {
-                $aStringTable = $pExistingTable;
-            }
-
-            // Fill index array
-            $aFlippedStringTable = $this->flipStringTable($aStringTable);
-
-            // Loop through cells
-            foreach ($pSheet->getCoordinates() as $coordinate) {
-                $cell = $pSheet->getCell($coordinate);
-                $cellValue = $cell->getValue();
-                if (!is_object($cellValue) &&
-                    ($cellValue !== null) &&
-                    $cellValue !== '' &&
-                    !isset($aFlippedStringTable[$cellValue]) &&
-                    ($cell->getDataType() == Cell\DataType::TYPE_STRING || $cell->getDataType() == Cell\DataType::TYPE_STRING2 || $cell->getDataType() == Cell\DataType::TYPE_NULL)) {
-                    $aStringTable[] = $cellValue;
-                    $aFlippedStringTable[$cellValue] = true;
-                } elseif ($cellValue instanceof RichText &&
-                          ($cellValue !== null) &&
-                          !isset($aFlippedStringTable[$cellValue->getHashCode()])) {
-                    $aStringTable[] = $cellValue;
-                    $aFlippedStringTable[$cellValue->getHashCode()] = true;
-                }
-            }
-
-            return $aStringTable;
+        // Is an existing table given?
+        if (($pExistingTable !== null) && is_array($pExistingTable)) {
+            $aStringTable = $pExistingTable;
         }
 
-        throw new WriterException('Invalid Worksheet object passed.');
+        // Fill index array
+        $aFlippedStringTable = $this->flipStringTable($aStringTable);
+
+        // Loop through cells
+        foreach ($pSheet->getCoordinates() as $coordinate) {
+            $cell = $pSheet->getCell($coordinate);
+            $cellValue = $cell->getValue();
+            if (!is_object($cellValue) &&
+                ($cellValue !== null) &&
+                $cellValue !== '' &&
+                !isset($aFlippedStringTable[$cellValue]) &&
+                ($cell->getDataType() == Cell\DataType::TYPE_STRING || $cell->getDataType() == Cell\DataType::TYPE_STRING2 || $cell->getDataType() == Cell\DataType::TYPE_NULL)) {
+                $aStringTable[] = $cellValue;
+                $aFlippedStringTable[$cellValue] = true;
+            } elseif ($cellValue instanceof RichText &&
+                ($cellValue !== null) &&
+                !isset($aFlippedStringTable[$cellValue->getHashCode()])) {
+                $aStringTable[] = $cellValue;
+                $aFlippedStringTable[$cellValue->getHashCode()] = true;
+            }
+        }
+
+        return $aStringTable;
     }
 
     /**
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php
index 20e71d81..7698b4c0 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php
@@ -10,7 +10,7 @@ use PHPUnit_Framework_TestCase;
 class ColumnCellIteratorTest extends PHPUnit_Framework_TestCase
 {
     public $mockWorksheet;
-    public $mockColumnCell;
+    public $mockCell;
 
     public function setUp()
     {
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php
index 7a040862..2b42138b 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php
@@ -10,7 +10,7 @@ use PHPUnit_Framework_TestCase;
 class RowCellIteratorTest extends PHPUnit_Framework_TestCase
 {
     public $mockWorksheet;
-    public $mockRowCell;
+    public $mockCell;
 
     public function setUp()
     {