diff --git a/src/Calc/Formel.php b/src/Calc/Formel.php
index 6fef875..485eb4f 100644
--- a/src/Calc/Formel.php
+++ b/src/Calc/Formel.php
@@ -145,7 +145,11 @@ class Formel
                             if ($variables [$foundvalue] == '') {
                                 $formel = str_replace($found, 0, $formel);
                             } else {
-                                $formel = str_replace($found, $variables [$foundvalue], $formel);
+                                if(is_array($variables [$foundvalue])) {
+                                    $formel = str_replace($found, 0, $formel);
+                                }else{
+                                    $formel = str_replace($found, $variables [$foundvalue], $formel);
+                                }
                             }
                         }
                     }
diff --git a/tests/Customer/U/CalcTest.php b/tests/Customer/U/CalcTest.php
new file mode 100644
index 0000000..3bda9f5
--- /dev/null
+++ b/tests/Customer/U/CalcTest.php
@@ -0,0 +1,46 @@
+<?php
+namespace PSC\Library\Calc\Tests\Customer\U;
+
+use PHPUnit\Framework\TestCase;
+use PSC\Library\Calc\Article;
+use PSC\Library\Calc\Engine;
+use PSC\Library\Calc\PaperContainer;
+use PSC\Library\Calc\Tests\Mock\PaperRepostory;
+
+class CalcTest extends TestCase
+{
+
+    /** @var Engine */
+    protected $engine = null;
+
+    public function setUp(): void
+    {
+        $repository = new PaperRepostory();
+
+        $paperContainer = new PaperContainer();
+        $paperContainer->parse(simplexml_load_string(file_get_contents(__DIR__ . '/papierContainer.xml')));
+
+        $this->engine = new Engine();
+        $this->engine->setPaperContainer($paperContainer);
+        $this->engine->setPaperRepository($repository);
+        $this->engine->setFormulas(file_get_contents(__DIR__ . '/formels.txt'));
+        $this->engine->setParameters(file_get_contents(__DIR__ . '/parameters.txt'));
+        $this->engine->setTemplates(file_get_contents(__DIR__ . '/calcTemplates.xml'));
+
+        $this->engine->loadString(file_get_contents(__DIR__ . '/calc.xml'));
+
+    }
+
+    public function tearDown(): void
+    {
+        $this->engine = null;
+    }
+
+    public function testIfDefaultPriceIsOk(): void
+    {
+        $this->engine->calc();
+        $this->assertEquals(202 , $this->engine->getPrice());
+        $this->assertEquals('135 g/m² Bilderdruck matt gestrichen', $this->engine->getArticle()->getOptionById('papier')->getValue());
+
+    }
+}
diff --git a/tests/Customer/U/calc.xml b/tests/Customer/U/calc.xml
new file mode 100644
index 0000000..830bec9
--- /dev/null
+++ b/tests/Customer/U/calc.xml
@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- ACHTUNG STA+ PRÄ verwendet wegen "A < 682 cm2 Problem" hier IMMER den Fixwert von Fischer statt Tiegel  -->
+<kalkulation>
+    <artikel>
+        <name>Banderolen</name>
+        <kommentar/>
+
+        <option id="auflage" name="Auflage" type="Input" default="4" min="1" max="50000"/>
+
+        <option id="papier" name="Papier" type="Select" mode="papierdb" container="test_1" default="INM135ND">
+        </option>
+
+        <option id="calc_formel" name="calc_formel" type="Hidden" default="1">
+            <auflage>
+                <grenze formel="$Vauflage$V*$Vpapier_value$V">1-</grenze>
+            </auflage>
+        </option>
+    </artikel>
+</kalkulation>
\ No newline at end of file
diff --git a/tests/Customer/U/calcTemplates.xml b/tests/Customer/U/calcTemplates.xml
new file mode 100644
index 0000000..b3f7d62
--- /dev/null
+++ b/tests/Customer/U/calcTemplates.xml
@@ -0,0 +1,4 @@
+<root>
+
+
+</root>
diff --git a/tests/Customer/U/formels.txt b/tests/Customer/U/formels.txt
new file mode 100644
index 0000000..e69de29
diff --git a/tests/Customer/U/papierContainer.xml b/tests/Customer/U/papierContainer.xml
new file mode 100644
index 0000000..2697401
--- /dev/null
+++ b/tests/Customer/U/papierContainer.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<container>
+    <papiercontainer id="test_1">
+        <papier id="INM135"/>
+        <papier id="INM115"/>
+        <papier id="INM135ND"/>
+    </papiercontainer>
+</container>
\ No newline at end of file
diff --git a/tests/Customer/U/parameters.txt b/tests/Customer/U/parameters.txt
new file mode 100644
index 0000000..e69de29