The Windows 10 calculator is a getting a new feature that allows you to show it always on top of other windows that may be open. Microsoft senior program manager Dave Grochocki has stated that this feature is the second most requested one in the Feedback Hub. The always-on-top mode has been implemented in the GitHub project’s source code so anyone can download, compile, and test the new feature. It is not known when this will make it into an actual Windows 10 distribution.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-calculator-getting-always-on-top-mode-compact-version/