Mac external display problems

These pages are written one problem at a time, in the words you would actually search for. Each one explains the mechanism first, then what to do — including when the answer is not our app.

The display will not do what you ask

• For developers: what an implementation has to get right What a diagnostic report contains (and what it never does) When two apps fight over the same setting Which layer is dimming your screen What a gamma table actually does How to actually test a display Was it the update? Brightness keys do nothing on the external monitor — DDC/CI does not answer: why the panel, the cable or the port is the usual culprit, and what to try in order.
• Brightness resets after sleep — You dim it, close the lid, come back and it is bright again. What actually loses the value, and how to keep it.
• How do I change the brightness of an external display? — three ways, in the order worth trying, and what to do when none of them work.
• Dimming on a schedule walks the screen to black — the multiplier that compounds, the heartbeat that stops when you drag a slider, and why idempotence is the whole trick.

It looks wrong

• Text looks blurry or soft — The same resolution often exists twice — once with HiDPI scaling, once 1:1. How to tell them apart.
• Colours look washed out or flat — Two different complaints, one explanation: what dimming does to the colour you set, and how to get it back.

Input does not feel right

• Mouse-wheel scrolling feels jerky — macOS gives a wheel discrete clicks while a trackpad gets gestures. The mechanism that fixes it, and the three traps.
• Mouse acceleration will not stay off — the usual advice moves one of two layers. Measured values, and the API name that does not exist.

Housekeeping, done safely

• Clearing caches without losing anything — Where the tens of gigabytes actually are, and the one rule that makes cleanup reversible.

Choosing a tool, and checking us

• Which Mac display app should you use? — An honest comparison of the four apps in this space, including where ours is the wrong choice.
• Verify it yourself — We are new and we have no reviews. Here is how to check the download, the signature and the payment before trusting anything.
• How we audit this product — The measurements behind the claims on this site, and the ones we are not making.