---
title: "system.math.meanDifference"
description: "Given two sequences of values, calculates the mean of the signed difference between both sequences."
---

# system.math.meanDifference

> Given two sequences of values, calculates the mean of the signed difference between both sequences.

This function is used in **Python Scripting**.

## Description
Given two sequences of values, calculates the mean of the signed difference between both sequences. In other words, returns the absolute difference between the mean values of two different sets of data.

Throws a DimensionMismatchException if the two sequences have different lengths.

## Client Permission Restrictions
This scripting function has no [Client Permission](../../../ignition-modules/vision/vision-project-properties/vision-project-properties.md#vision-permissions-properties) restrictions.

## Syntax
`system.math.meanDifference(values1, values2)`

### Parameters
Type | Parameter | Description 
------- | ------- | ------
List[Float]| `values1` | A sequence of numerical values. Accepts both integers and floats. The sequence may not contain None type values. However, passing a None type object instead of a sequence of numerical values will return NaN.
List[Float]| `values2` | A sequence of numerical values. Accepts both integers and floats. The sequence may not contain None type values. However, passing a None type object instead of a sequence of numerical values will return NaN.

### Returns
**Float** - The mean difference, or NaN if one of the parameters was empty or null.

### Scope
Gateway, Vision Client, Perspective Session

## Code Examples
```python title="Example #1 - Calculating Mean Difference"
# Create some lists.
firstList = [3.5, 5.6, 7.8, 7.4, 3.8]
secondList = [3.5, 5.6, -7.8, 7.4, -3.8]
    
# Prints the resulting value.
print system.math.meanDifference(firstList, secondList)
```