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Selector Widgets are a group of widgets that let you create report-level settings. They let you select the account/campaign/label which you would like to report on for your choice of the date range. This segment also offers to add custom metrics using Calculated Metrics.

This widget lets you choose and add the date range of your choice. You can either use a date range that is relative or define a custom date range. You can also insert a custom date range in the report body. 

In the Report Designer, you'll see the 'Campaign Selector' option in the widgets table. This will let you add multiple accounts and select the level at which you want to report at - label or campaign level or entire account level. 

You can add multiple campaign picker widgets for the same account, and select different labels and campaigns. If you add more than one campaign selector in the Report template you will have to configure the individual widgets to fetch data from the right data set.

In the Report Designer, you'll see the 'Account Picker' option in the widgets table. This will let you add multiple accounts and select the level at which you want to report at - account, label, or campaign level. 

You can add multiple account picker widgets for the same account, and select different labels and campaigns. Each account picker added will show up in individual widgets. Account Selector is available only on Pro and Enterprise plan in the Multi-Account Reports.

The Calculated Metrics widget allows you to add custom parameters as columns in all the table widgets in the reports. To use this feature, access Multi-Account Reporting. 

Read more on how to add calculated metrics here.