# OH3 User Interface: From beginner for beginners **URL:** \ **Category:** openHAB Stories\ **Tags:** ui, beginners\ **Created:** [April 21, 2021, 7:19am UTC](https://community.openhab.org/t/oh3-user-interface-from-beginner-for-beginners/121149 "2021-04-21T07:19:45Z")\ **Posts on this page:** 1\ **Showing post:** 10
**Author:** ![hmerk](https://community.openhab.org/user_avatar/community.openhab.org/hmerk/32/56432_2.png) [@hmerk](https://community.openhab.org/u/hmerk)\ **Post date:** [April 21, 2021, 5:39pm UTC](https://community.openhab.org/t/oh3-user-interface-from-beginner-for-beginners/121149/10 "2021-04-21T17:39:03Z")
> [@Ursusprimus](#): > > the number of running lights is derived from an item whose value is calculated with a rule (see below YMAL code) You might check the following, makes your rules obsolete… > [@CustomWidget PopOver - Item from parameter does not use the configuration of the specific widget, but the last widget](https://community.openhab.org/t/customwidget-popover-item-from-parameter-does-not-use-the-configuration-of-the-specific-widget-but-the-last-widget/113980/28): > > Sure wink That’s a good question, since the solution is not that obvious in openHAB3 wink When checking the documentation for aggregation functions you may have noticed the COUNT() aggregation: Unfortunately, the COUNT() aggregator is not selectable in the MainUI of openHAB3. BUT: You can work around that limitation by importing group items with COUNT() aggregators from textual configuration: This essentially adds two groups where one counts for empty and another count for … --- _[View the full topic](https://community.openhab.org/t/oh3-user-interface-from-beginner-for-beginners/121149)._