As probably you have read before, you can decide which project fields you want to display per project in the Layouts. The layouts are like the project schemes in Jira.
Associate a layout to one or more projects
1. From the layout manager click on Associate
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After click on "Associate projects" you just need to select all the projects you want to have that layout, and save.
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Switch layout in one project
You can change the project layout in the project tab. If you switch to another layout you don't lose the values of the fields.
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After click in "Switch layout" you can choose from the different layouts created.
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