Hi List members We have been profiling the display in our labs for many years now. This year we have refreshed many of our leased computers with 2017 27inch iMac retina 5K (model identifier 18.3). We are experiencing this issue with JUST the new 2017 iMac hardware (v18.3) running OS 10.13.3 (and .2). Not our older iMacs. Is anyone else having problems (outlined below). Or is it just us? The issue In Brief When i1Profiler adjusts the display brightness to our 120cdm target using automatic display adjustment (ADC) the screen brightness changes just as I would expect it to. However on our new 2017 27inch iMac retina 5K (model identifier 18.3), the OS is not updating the position of the brightness slider in the user interface of the System Preference / Displays to reflect the changes made by i1Profiles ADC. So the position of the brightness slider in the user interface stays in it’s earlier uncalibrated state. After i1profiler reads the patches there is a “verify” step. Something in the verify step is causing the OS to touch the System Preference / Display pane. The OS then sees the (unmoved) position of the brightness slider in the user interface and forces the display back to it. i1 profiler then measures this and reports it as the achieved target brightness. A Quick Test. If someone with a 2017 27 inch iMac (v18.3) with i1Profiler wants to run this test can they email to let me know they find. - Set system preference brightness slider to 100. - set target brightness in i1Profiler to 120 cdm - run i1profiler using ADC. ( the screen should get dimmed) - watch carefully during the Verify step. - Do you see the brightness of the screen suddenly jump back to 100? Please kindly let me know. Thanks for your help. Regards Peter Miles PS : Manual adjusting not working either. I tried to use the manual brightness adjustment method in i1Profiler to bypass this bug / issue. But on these new machines that does not work as the System preferences pane can’t be brought to the foreground when i1Pofiler has got the measurement window up.