The "1:1" icon is added automatically.

When clicked for the first time (or then when double-clicked), it will prompt you to zoom your object manually to a known true size.

Then it will use the same zoom ratio automatically.

It is intended to be used for orthographic views of your design files.

Install:
The installer that ran when you downloaded this app/plug-in from the Autodesk App Store will start installing the app/plug-in. Or, simply double-click the downloaded installer to install the app/plugin.

Uninstall:
You can unload the add-in without uninstalling it by clicking the "Stop" button when the add-in is selected in the list box on the "Add-Ins" tab of the "Scripts and Add-Ins" dialog.
Unchecking "Run on Startup" causes the add-in not to be loaded in future sessions of Fusion.
To uninstall this plug-in, exit the Autodesk product if you are currently running it, simply rerun the installer, and select the "Uninstall" button.
Or, you can uninstall it from 'Control Panel/Programs and Features' (Windows 10/11), just as you would uninstall any other application from your system.

License: View11 is a freeware version of a utility by ARKANCE (includes Python code).