This page documents the LookML parameters to apply a reference line to a LookML dashboard tile. They work for all charts, except bar charts, and those where `swap_axes`

has been set to true.

Reference lines allow you to place **lines** and **regions** on any of Looker’s cartesian charts. You can use static values, or certain statistical functions computed from the chart’s data.

## Configuration

Reference lines are specified as an option in the dashboard configuration for Looker’s scatter, area, line, column, and bar charts.

Reference lines are currently only supported on the first series of these charts.

You can have an unlimited number of reference lines on any chart.

The `reference_lines`

configuration option takes an array of reference lines, each item of which is a hash of options.

The configuration option for the above chart is implemented like this:

```
reference_lines:
- value: 90
label: Sales Goal
color: crimson
```

## Drawing a Constant Line

`value`

is the only required field for a reference line. It specifies where there reference should be drawn.

To draw a single line at the “50” mark on the chart, specify your configuration like this:

```
reference_lines:
- value: 50
```

## Value Calculations

Instead of specifying a number for your reference line value, you can also specify a **calculation name**.

All value calculations are based on *the dataset returned from the query*, not your entire dataset.

`median`

- The median value of the dataset.`mean`

- The average value of the dataset.`max`

- The maximum value of the dataset.`min`

- The minimum value of the dataset.`deviation`

- The standard deviation of the dataset.`variance`

- The statistical variance of the dataset.

To draw a line at the median value of your dataset, it’s as simple as this.

```
reference_lines:
- value: median
```

To draw three lines, one at the median, one at a constant value, and one at the maxiumum you would specify your configuration like this:

```
reference_lines:
- value: median
- value: 25
- value: max
```

## Drawing an Area

Instead of specifying a single number or calculation name for your reference line, you can also provide an array.

If the provided array has exactly two values, it’s treated as the bounds of a range.

```
reference_lines:
- value: [60, 90]
label: Butter Zone
color: orange
```

This can become very powerful when combined with the value calculations.

The following configuration will shade an area that represents an area where data points are above the average.

```
reference_lines:
- value: [max, mean]
label: Above Average
```

## Lines and Errors

You can also provide an array of three numbers or calculation names to the `value`

parameter.

In this configuration, the first value is treated as the error “below” the reference line, the middle value is considered the value for the line itself, and the third value is treated as the error “above” the reference line.

```
error below, reference line value, error above
```

Let’s say your sales goal is 60 units, but +/- 5 units is in the acceptable range. You could illustrate this on a graph like this:

```
reference_lines:
- value: [5, 60, 5]
label: Target Sales
```

This, too, gets interesting with calculations.

Here’s how you could specify the average showing the standard deviation:

```
reference_lines:
- value: [deviation, mean, deviation]
```

## Labels

You can also include a `label`

attribute to label the line with text of your choice.

```
reference_lines:
- value: 90
label: Sales Goal
```

You can also choose to include calculated values in your label, whether or not you use them on your chart.

Simply place the calculation name inside double curly braces: `{{median}}`

. You will have to place quotation marks around your label string if you do this.

```
reference_lines:
- value: 50
label: "Target (Average: {{mean}})"
```

## Colors

You can also include a `color`

attribute to color the line and text however you wish.

Color values can each be a hex string like `#2ca6cd`

or a CSS named color string.