diff --git a/src/Calculator.php b/src/Calculator.php
index b5c6eff..d51ab95 100644
--- a/src/Calculator.php
+++ b/src/Calculator.php
@@ -38,7 +38,7 @@ public function statistics(array $values) {
 			'max' => 0
 		);
 		foreach ($values as $set) {
-			$value = $set['value'];
+			$value = (float) $set['value'];
 			$data['sum'] += $value;
 			if ($data['min'] === NULL || $value < $data['min']) {
 				$data['min'] = $value;
diff --git a/tests/Unit/CalculatorTest.php b/tests/Unit/CalculatorTest.php
index acbfe3e..2952a35 100644
--- a/tests/Unit/CalculatorTest.php
+++ b/tests/Unit/CalculatorTest.php
@@ -1,5 +1,6 @@
 <?php
 namespace NamelessCoder\Numerolog\Tests\Unit;
+use NamelessCoder\Numerolog\Calculator;
 
 /**
  * Class CalculatorTest
@@ -7,10 +8,86 @@
 class CalculatorTest extends \PHPUnit_Framework_TestCase {
 
 	/**
-	 * @test
+	 * @param float $value
+	 * @param boolean $expected
+	 * @dataProvider getIsSignedTestValues
 	 */
-	public function testMarkIncomplete() {
-		$this->markTestIncomplete('Not yet implemented');
+	public function testIsSigned($value, $expected) {
+		$calculator = new Calculator();
+		$this->assertEquals($expected, $calculator->isSigned($value));
+	}
+
+	/**
+	 * @return array
+	 */
+	public function getIsSignedTestValues() {
+		return array(
+			array(1, FALSE),
+			array(-1, TRUE),
+			array(0.514, FALSE),
+			array(-0.132, TRUE)
+		);
+	}
+
+	/**
+	 * @param float $value
+	 * @param mixed $modification
+	 * @param float $expected
+	 * @dataProvider getModifyTestValues
+	 */
+	public function testModify($value, $modification, $expected) {
+		$calculator = new Calculator();
+		$this->assertEquals($expected, $calculator->modify($value, $modification));
+	}
+
+	/**
+	 * @return array
+	 */
+	public function getModifyTestValues() {
+		return array(
+			array(1, 2, 2),
+			array(1, '+1', 2),
+			array(2, -1, 1)
+		);
+	}
+
+	/**
+	 * @param array $values
+	 * @param array $expected
+	 * @dataProvider getStatisticsTestValues
+	 */
+	public function testStatistics(array $values, array $expected) {
+		$calculator = new Calculator();
+		$this->assertEquals($expected, $calculator->statistics($values));
+	}
+
+	/**
+	 * @return array
+	 */
+	public function getStatisticsTestValues() {
+		return array(
+			array(
+				array(
+					array('value' => 1),
+					array('value' => 2),
+					array('value' => 3),
+					array('value' => 4),
+					array('value' => 5)
+				),
+				array('min' => 1, 'max' => 5, 'sum' => 15, 'average' => 3, 'count' => 5)
+			),
+			array(
+				array(
+					array('value' => 0.4),
+					array('value' => 1.2),
+					array('value' => 2.4),
+					array('value' => 3.8),
+					array('value' => 0.5)
+				),
+				array('min' => 0.4, 'max' => 3.8, 'sum' => 8.3, 'average' => 1.66, 'count' => 5)
+			),
+
+		);
 	}
 
 }