How can I keep two displays at similar brightness?

Use Synchronize brightness nits to make displays follow the same calculated luminance. Matching brightness percentages alone can produce very different results on panels with different brightness ranges. Nits synchronization requires Pro and working brightness controllers on the participating displays.

1. Open Settings > Groups and choose an active group containing the displays.
2. Open Synchronization Settings and enable Enable synchronization for this display group.
3. Add or edit the Brightness entry, enable its synchronization, and turn on Synchronize brightness nits.
4. Allow the intended display to act as a source and the others to receive its changes.
5. Review each display’s General Settings > Configure Brightness Nits Ranges…. Use reliable display data or measurements for any manual overrides, then compare the screens at several brightness levels.

This matches calculated nits. It is not a per-step table where you assign a separate brightness value for every slider position. Incorrect brightness anchors can make the match inaccurate, and a target cannot reproduce a level beyond its physical capabilities. HDR behavior, picture settings and the content on screen can also affect the comparison. See nits readings and manual ranges before changing those values.

Follow Match brightness across different monitors for a complete comparison of percentage and nits synchronization, explicit source and receiver selection, endpoint review and restoration.

To follow changes detected outside BetterDisplay, such as automatic brightness, enable Synchronize changes triggered externally. The source controller must be able to detect those changes. The automatic external brightness answer explains that setup.

Test synchronization with the source display’s menu slider. Brightness keys set to All suitable screens adjust the displays directly and bypass group brightness synchronization for that operation. See Synchronization Settings for source and target filters.