diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -2817,6 +2817,7 @@
     'PhabricatorCoreCreateTransaction' => 'applications/transactions/xaction/PhabricatorCoreCreateTransaction.php',
     'PhabricatorCoreTransactionType' => 'applications/transactions/xaction/PhabricatorCoreTransactionType.php',
     'PhabricatorCoreVoidTransaction' => 'applications/transactions/xaction/PhabricatorCoreVoidTransaction.php',
+    'PhabricatorCosChartFunction' => 'applications/fact/chart/PhabricatorCosChartFunction.php',
     'PhabricatorCountFact' => 'applications/fact/fact/PhabricatorCountFact.php',
     'PhabricatorCountdown' => 'applications/countdown/storage/PhabricatorCountdown.php',
     'PhabricatorCountdownApplication' => 'applications/countdown/application/PhabricatorCountdownApplication.php',
@@ -4475,6 +4476,7 @@
     'PhabricatorSSHWorkflow' => 'infrastructure/ssh/PhabricatorSSHWorkflow.php',
     'PhabricatorSavedQuery' => 'applications/search/storage/PhabricatorSavedQuery.php',
     'PhabricatorSavedQueryQuery' => 'applications/search/query/PhabricatorSavedQueryQuery.php',
+    'PhabricatorScaleChartFunction' => 'applications/fact/chart/PhabricatorScaleChartFunction.php',
     'PhabricatorScheduleTaskTriggerAction' => 'infrastructure/daemon/workers/action/PhabricatorScheduleTaskTriggerAction.php',
     'PhabricatorScopedEnv' => 'infrastructure/env/PhabricatorScopedEnv.php',
     'PhabricatorSearchAbstractDocument' => 'applications/search/index/PhabricatorSearchAbstractDocument.php',
@@ -4564,6 +4566,7 @@
     'PhabricatorSetupIssue' => 'applications/config/issue/PhabricatorSetupIssue.php',
     'PhabricatorSetupIssueUIExample' => 'applications/uiexample/examples/PhabricatorSetupIssueUIExample.php',
     'PhabricatorSetupIssueView' => 'applications/config/view/PhabricatorSetupIssueView.php',
+    'PhabricatorShiftChartFunction' => 'applications/fact/chart/PhabricatorShiftChartFunction.php',
     'PhabricatorShortSite' => 'aphront/site/PhabricatorShortSite.php',
     'PhabricatorShowFiletreeSetting' => 'applications/settings/setting/PhabricatorShowFiletreeSetting.php',
     'PhabricatorSimpleEditType' => 'applications/transactions/edittype/PhabricatorSimpleEditType.php',
@@ -8811,6 +8814,7 @@
     'PhabricatorCoreCreateTransaction' => 'PhabricatorCoreTransactionType',
     'PhabricatorCoreTransactionType' => 'PhabricatorModularTransactionType',
     'PhabricatorCoreVoidTransaction' => 'PhabricatorModularTransactionType',
+    'PhabricatorCosChartFunction' => 'PhabricatorChartFunction',
     'PhabricatorCountFact' => 'PhabricatorFact',
     'PhabricatorCountdown' => array(
       'PhabricatorCountdownDAO',
@@ -10775,6 +10779,7 @@
       'PhabricatorPolicyInterface',
     ),
     'PhabricatorSavedQueryQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
+    'PhabricatorScaleChartFunction' => 'PhabricatorChartFunction',
     'PhabricatorScheduleTaskTriggerAction' => 'PhabricatorTriggerAction',
     'PhabricatorScopedEnv' => 'Phobject',
     'PhabricatorSearchAbstractDocument' => 'Phobject',
@@ -10864,6 +10869,7 @@
     'PhabricatorSetupIssue' => 'Phobject',
     'PhabricatorSetupIssueUIExample' => 'PhabricatorUIExample',
     'PhabricatorSetupIssueView' => 'AphrontView',
+    'PhabricatorShiftChartFunction' => 'PhabricatorChartFunction',
     'PhabricatorShortSite' => 'PhabricatorSite',
     'PhabricatorShowFiletreeSetting' => 'PhabricatorSelectSetting',
     'PhabricatorSimpleEditType' => 'PhabricatorEditType',
diff --git a/src/applications/fact/chart/PhabricatorChartFunction.php b/src/applications/fact/chart/PhabricatorChartFunction.php
--- a/src/applications/fact/chart/PhabricatorChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorChartFunction.php
@@ -5,9 +5,9 @@
 
   private $xAxis;
   private $yAxis;
-  private $limit;
 
   private $argumentParser;
+  private $sourceFunction;
 
   final public function getFunctionKey() {
     return $this->getPhobjectClassConstant('FUNCTIONKEY', 32);
@@ -44,6 +44,12 @@
     $parser->setHaveAllArguments(true);
     $parser->parseArguments();
 
+    $source_argument = $parser->getSourceFunctionArgument();
+    if ($source_argument) {
+      $source_function = $this->getArgument($source_argument->getName());
+      $this->setSourceFunction($source_function);
+    }
+
     return $this;
   }
 
@@ -71,6 +77,15 @@
     return;
   }
 
+  protected function setSourceFunction(PhabricatorChartFunction $source) {
+    $this->sourceFunction = $source;
+    return $this;
+  }
+
+  protected function getSourceFunction() {
+    return $this->sourceFunction;
+  }
+
   final public function setXAxis(PhabricatorChartAxis $x_axis) {
     $this->xAxis = $x_axis;
     return $this;
@@ -89,6 +104,67 @@
     return $this->yAxis;
   }
 
+  protected function canEvaluateFunction() {
+    return false;
+  }
+
+  protected function evaluateFunction($x) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function hasDomain() {
+    if ($this->canEvaluateFunction()) {
+      return false;
+    }
+
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getDatapoints(PhabricatorChartDataQuery $query) {
+    if ($this->canEvaluateFunction()) {
+      $points = $this->newSourceDatapoints($query);
+      foreach ($points as $key => $point) {
+        $y = $point['y'];
+        $y = $this->evaluateFunction($y);
+        $points[$key]['y'] = $y;
+      }
+
+      return $points;
+    }
+
+    return $this->newDatapoints($query);
+  }
+
+  protected function newDatapoints(PhabricatorChartDataQuery $query) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  protected function newSourceDatapoints(PhabricatorChartDataQuery $query) {
+    $source = $this->getSourceFunction();
+    if ($source) {
+      return $source->getDatapoints($query);
+    }
+
+    return $this->newDefaultDatapoints($query);
+  }
+
+  protected function newDefaultDatapoints(PhabricatorChartDataQuery $query) {
+    $x_min = $query->getMinimumValue();
+    $x_max = $query->getMaximumValue();
+    $limit = $query->getLimit();
+
+    $points = array();
+    $steps = $this->newLinearSteps($x_min, $x_max, $limit);
+    foreach ($steps as $step) {
+      $points[] = array(
+        'x' => $step,
+        'y' => $step,
+      );
+    }
+
+    return $points;
+  }
+
   protected function newLinearSteps($src, $dst, $count) {
     $count = (int)$count;
     $src = (int)$src;
diff --git a/src/applications/fact/chart/PhabricatorChartFunctionArgument.php b/src/applications/fact/chart/PhabricatorChartFunctionArgument.php
--- a/src/applications/fact/chart/PhabricatorChartFunctionArgument.php
+++ b/src/applications/fact/chart/PhabricatorChartFunctionArgument.php
@@ -5,6 +5,7 @@
 
   private $name;
   private $type;
+  private $isSourceFunction;
 
   public function setName($name) {
     $this->name = $name;
@@ -39,6 +40,15 @@
     return $this->type;
   }
 
+  public function setIsSourceFunction($is_source_function) {
+    $this->isSourceFunction = $is_source_function;
+    return $this;
+  }
+
+  public function getIsSourceFunction() {
+    return $this->isSourceFunction;
+  }
+
   public function newValue($value) {
     switch ($this->getType()) {
       case 'fact-key':
diff --git a/src/applications/fact/chart/PhabricatorChartFunctionArgumentParser.php b/src/applications/fact/chart/PhabricatorChartFunctionArgumentParser.php
--- a/src/applications/fact/chart/PhabricatorChartFunctionArgumentParser.php
+++ b/src/applications/fact/chart/PhabricatorChartFunctionArgumentParser.php
@@ -151,4 +151,43 @@
       implode(', ', $argument_list));
   }
 
+  public function getSourceFunctionArgument() {
+    $required_type = 'function';
+
+    $sources = array();
+    foreach ($this->argumentMap as $key => $argument) {
+      if (!$argument->getIsSourceFunction()) {
+        continue;
+      }
+
+      if ($argument->getType() !== $required_type) {
+        throw new Exception(
+          pht(
+            'Function "%s" defines an argument "%s" which is marked as a '.
+            'source function, but the type of this argument is not "%s".',
+            $this->getFunctionArgumentSignature(),
+            $argument->getName(),
+            $required_type));
+      }
+
+      $sources[$key] = $argument;
+    }
+
+    if (!$sources) {
+      return null;
+    }
+
+    if (count($sources) > 1) {
+      throw new Exception(
+        pht(
+          'Function "%s" defines more than one argument as a source '.
+          'function (arguments: %s). Functions must have zero or one '.
+          'source function.',
+          $this->getFunctionArgumentSignature(),
+          implode(', ', array_keys($sources))));
+    }
+
+    return head($sources);
+  }
+
 }
diff --git a/src/applications/fact/chart/PhabricatorConstantChartFunction.php b/src/applications/fact/chart/PhabricatorConstantChartFunction.php
--- a/src/applications/fact/chart/PhabricatorConstantChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorConstantChartFunction.php
@@ -5,8 +5,6 @@
 
   const FUNCTIONKEY = 'constant';
 
-  private $value;
-
   protected function newArguments() {
     return array(
       $this->newArgument()
@@ -15,26 +13,12 @@
     );
   }
 
-  public function getDatapoints(PhabricatorChartDataQuery $query) {
-    $x_min = $query->getMinimumValue();
-    $x_max = $query->getMaximumValue();
-
-    $value = $this->getArgument('n');
-
-    $points = array();
-    $steps = $this->newLinearSteps($x_min, $x_max, 2);
-    foreach ($steps as $step) {
-      $points[] = array(
-        'x' => $step,
-        'y' => $value,
-      );
-    }
-
-    return $points;
+  protected function canEvaluateFunction() {
+    return true;
   }
 
-  public function hasDomain() {
-    return false;
+  protected function evaluateFunction($x) {
+    return $this->getArgument('n');
   }
 
 }
diff --git a/src/applications/fact/chart/PhabricatorCosChartFunction.php b/src/applications/fact/chart/PhabricatorCosChartFunction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/fact/chart/PhabricatorCosChartFunction.php
@@ -0,0 +1,25 @@
+<?php
+
+final class PhabricatorCosChartFunction
+  extends PhabricatorChartFunction {
+
+  const FUNCTIONKEY = 'cos';
+
+  protected function newArguments() {
+    return array(
+      $this->newArgument()
+        ->setName('x')
+        ->setType('function')
+        ->setIsSourceFunction(true),
+    );
+  }
+
+  protected function canEvaluateFunction() {
+    return true;
+  }
+
+  protected function evaluateFunction($x) {
+    return cos(deg2rad($x));
+  }
+
+}
diff --git a/src/applications/fact/chart/PhabricatorScaleChartFunction.php b/src/applications/fact/chart/PhabricatorScaleChartFunction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/fact/chart/PhabricatorScaleChartFunction.php
@@ -0,0 +1,28 @@
+<?php
+
+final class PhabricatorScaleChartFunction
+  extends PhabricatorChartFunction {
+
+  const FUNCTIONKEY = 'scale';
+
+  protected function newArguments() {
+    return array(
+      $this->newArgument()
+        ->setName('x')
+        ->setType('function')
+        ->setIsSourceFunction(true),
+      $this->newArgument()
+        ->setName('scale')
+        ->setType('number'),
+    );
+  }
+
+  protected function canEvaluateFunction() {
+    return true;
+  }
+
+  protected function evaluateFunction($x) {
+    return $x * $this->getArgument('scale');
+  }
+
+}
diff --git a/src/applications/fact/chart/PhabricatorShiftChartFunction.php b/src/applications/fact/chart/PhabricatorShiftChartFunction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/fact/chart/PhabricatorShiftChartFunction.php
@@ -0,0 +1,28 @@
+<?php
+
+final class PhabricatorShiftChartFunction
+  extends PhabricatorChartFunction {
+
+  const FUNCTIONKEY = 'shift';
+
+  protected function newArguments() {
+    return array(
+      $this->newArgument()
+        ->setName('x')
+        ->setType('function')
+        ->setIsSourceFunction(true),
+      $this->newArgument()
+        ->setName('shift')
+        ->setType('number'),
+    );
+  }
+
+  protected function canEvaluateFunction() {
+    return true;
+  }
+
+  protected function evaluateFunction($x) {
+    return $x * $this->getArgument('shift');
+  }
+
+}
diff --git a/src/applications/fact/chart/PhabricatorSinChartFunction.php b/src/applications/fact/chart/PhabricatorSinChartFunction.php
--- a/src/applications/fact/chart/PhabricatorSinChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorSinChartFunction.php
@@ -9,26 +9,17 @@
     return array(
       $this->newArgument()
         ->setName('x')
-        ->setType('function'),
+        ->setType('function')
+        ->setIsSourceFunction(true),
     );
   }
 
-  protected function assignArguments(array $arguments) {
-    $this->argument = $arguments[0];
+  protected function canEvaluateFunction() {
+    return true;
   }
 
-  public function getDatapoints(PhabricatorChartDataQuery $query) {
-    $points = $this->getArgument('x')->getDatapoints($query);
-
-    foreach ($points as $key => $point) {
-      $points[$key]['y'] = sin(deg2rad($points[$key]['y']));
-    }
-
-    return $points;
-  }
-
-  public function hasDomain() {
-    return false;
+  protected function evaluateFunction($x) {
+    return sin(deg2rad($x));
   }
 
 }
diff --git a/src/applications/fact/chart/PhabricatorXChartFunction.php b/src/applications/fact/chart/PhabricatorXChartFunction.php
--- a/src/applications/fact/chart/PhabricatorXChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorXChartFunction.php
@@ -9,25 +9,12 @@
     return array();
   }
 
-  public function getDatapoints(PhabricatorChartDataQuery $query) {
-    $x_min = $query->getMinimumValue();
-    $x_max = $query->getMaximumValue();
-    $limit = $query->getLimit();
-
-    $points = array();
-    $steps = $this->newLinearSteps($x_min, $x_max, $limit);
-    foreach ($steps as $step) {
-      $points[] = array(
-        'x' => $step,
-        'y' => $step,
-      );
-    }
-
-    return $points;
+  protected function canEvaluateFunction() {
+    return true;
   }
 
-  public function hasDomain() {
-    return false;
+  protected function evaluateFunction($x) {
+    return $x;
   }
 
 }
diff --git a/src/applications/fact/controller/PhabricatorFactChartController.php b/src/applications/fact/controller/PhabricatorFactChartController.php
--- a/src/applications/fact/controller/PhabricatorFactChartController.php
+++ b/src/applications/fact/controller/PhabricatorFactChartController.php
@@ -29,6 +29,27 @@
     $functions[] = id(new PhabricatorSinChartFunction())
       ->setArguments(array($x_function));
 
+    $cos_function = id(new PhabricatorCosChartFunction())
+      ->setArguments(array($x_function));
+
+    $functions[] = id(new PhabricatorShiftChartFunction())
+      ->setArguments(
+        array(
+          array(
+            'scale',
+            array(
+              'cos',
+              array(
+                'scale',
+                array('x'),
+                0.001,
+              ),
+            ),
+            10,
+          ),
+          200,
+        ));
+
     list($domain_min, $domain_max) = $this->getDomain($functions);
 
     $axis = id(new PhabricatorChartAxis())
@@ -83,6 +104,9 @@
       'yMax' => $y_max,
     );
 
+    // TODO: Move this back up, it's just down here for now to make
+    // debugging easier so the main page throws a more visible exception when
+    // something goes wrong.
     if ($is_chart_mode) {
       return $this->newChartResponse();
     }