As a developer, you may want to see measurements in rem while inspecting the layers in your designs for Web projects.
You can enable rem and define a root font size from the right panel of the “Spacing & Layout” page of your styleguide. This way, Zeplin displays measurements and font sizes in rem while you are inspecting the layers and also in the code snippets.
You can also enable rem for measurements and font sizes separately based on your workflow. For example, if you enable rem just for font sizes, Zeplin keep displaying measurements in px but Font sizes in rem.
☝️If your project has been linked to a global styleguide, the rem settings in that styleguide will be valid for your project too. But, you can customize it just for your project from your project's styleguide. When you do this, you'll see an information note about overridden rem settings and you can revert it if you want.