Photo Ephemeris Web is not intended to be run in multiple browser windows or tabs simultaneously.
While most functions will perform normally in these circumstances, some - particularly anything related to changes in Saved Locations or Settings may exhibit inconsistent behaviour and/or errors.
If you need to have the web app open in more than window at the same time, it is recommended to use two different browsers (e.g. Safari and Chrome) or to use private browsing windows to keep things logically separated.
Note: please be aware that running the app in multiple windows will incur additional bandwidth and data usage (for you and us!)