What the CPU gauge in NotchStar shows

System stats Published 4 November 2026

All of help center Try NotchStar in the browser Buy for $4

The CPU ring in the NotchStar System tab shows how busy your whole Mac’s processor is, from 0 to 100 percent. Hover over the notch, pick System, and the ring updates once a second for as long as the tab is open.

How the number is made

NotchStar asks macOS for the processor’s tick counters, the same kind of counters Activity Monitor draws from. It compares two samples one second apart. The share of ticks spent on user work, system work and nice work, out of all ticks, is the percentage you see.

That means three things:

It is a total for the whole Mac. It is not per core and it is not per app, so it never goes above 100.
The first reading after you open the tab is 0, because there is nothing earlier to compare with. The next one is real.
It is a one second window. A short spike can show and be gone before you look.

What the colour means

The ring is the normal accent colour until usage passes 65 percent, when it turns orange. Above 85 percent it turns red. High usage is treated as the warning, so a busy Mac looks different from an idle one at a glance.

Which app is using it

The ring does not name a culprit. For that, open the Disk tab and its Monitor section, which lists the five busiest processes by CPU and the five using the most memory. Activity Monitor on your Mac goes further, with per process history and energy figures. See how NotchStar System compares with Activity Monitor.

The whole tool is described on the System stats feature page. To see what the other rings measure, read the memory gauge.

Quick answers.

Why does the CPU ring show 0 percent right after I open the tab?

The figure is the change between two samples. The first sample has nothing to compare with, so it reads 0. The next one, about a second later, is a real reading.

Link to this answer

Does the CPU gauge show one app?

No. It shows the whole Mac. For the busiest apps, open the Disk tab and its Monitor section.

Link to this answer

Keep reading.

CPU, memory, disk, battery and network: Live CPU, memory, disk, battery and network speed gauges in your Mac notch. Sampling only runs while the tab is open, so it stays light.
How often NotchStar updates system stats: The System tab samples once a second, and only while it is on screen. The Monitor section in Disk samples every 3 seconds, ports about every 9.
NotchStar System tab vs Activity Monitor: NotchStar gives five readings at a glance. Activity Monitor gives per process detail. What each shows, and when to open which.
What the memory gauge in NotchStar shows: The memory ring in NotchStar counts active, wired and compressed memory against your Mac's total RAM. Cached files are not counted.

Put your notch to work.

Buy it once for $4, activate it in a minute, and keep it. Not sure yet? Try every tool in the browser on the home page, or install the 7 day trial.

Buy NotchStar for $4 Try it in the browser