Sistrix Update Radar: what the SERP dynamics measure and what not

On 27 September 2026 the Sistrix Update Radar for Germany showed 136.34. For values above 6, Sistrix assumes a relevant Google update based on its own observations. The highest value in the 90-day course shown up to 26 September 2026 was 35.68.

I noticed it on 30 September 2026 while updating my article on the Semrush Sensor. I put the values of both tools side by side for the days of the September 2026 spam update. For Germany on 27 September, Semrush showed 6.2 on desktop, i.e. “High range”, and 2.8 on mobile. Sistrix showed a curve that shoots out of the chart.

Anyone who sees a number like that wants to know whether something big is happening. For that you need to know how the radar calculates. That is on the Sistrix page, but far below the chart. Here is what the value means, where it reaches its limits and how you cross-check it against the Semrush Sensor and your own data.

The Google Update Radar is a free tool from Sistrix. Sistrix introduced it on 19 August 2020, at the time only for Germany and based on smartphone search results. Today the country selection lists 13 markets, from Germany, Austria and Switzerland to Brazil and Turkey.

Sistrix describes the method on the radar page itself. According to Sistrix, the rankings for “many millions of keywords” are measured every day for the daily updated Visibility Index. The radar draws on this data and asks two things: how many of the recorded domains show an above-average change in visibility? And how strong are these shifts? An index value is calculated from both. Sistrix does not publish the exact formula it uses to combine the two.

This has two consequences. The radar is only as good as the ranking data underneath. And it shows movement across many domains, not the movement of your site.

Unlike the Semrush Sensor, the scale does not run from 0 to 10. According to its own description, Sistrix scales the index value “so that the average value over the last 90 days is one”. Below 1 means less is happening than on average, above 1 means more. Sistrix has fixed texts for four values:

Source: Sistrix Google Update Radar, texts classifying the SERP dynamics, retrieved on 30 September 2026.

Sistrix bases the threshold of 6 on “past observations”. That is a rule of thumb from the provider, not a rule of calculation. For comparison: during the Google bug in August 2020, the radar showed a value of over 11 according to Sistrix.

Now the part I stumbled over. If the 1 were the simple average of exactly the 90 values the chart shows, they would have to add up to 90. Since no daily value in the chart is below 0, the value of 136.34 on 27 September 2026 alone would, with 90 equally weighted values, already lead to a minimum average of around 1.51. A simple average of the visible values therefore cannot readily explain the reference. Whether Sistrix weights differently internally, uses a different period or processes the display differently is not described on the page. For you, this means: read the 1 as the provider’s reference value and the values as a comparison within the curve, not as an absolute number.

The values for the days around the September 2026 spam update, read from the chart:

Source: Sistrix Google Update Radar, tooltip values in the chart, read on 30 September 2026. Level according to the thresholds 1, 2 and 6 from the table above.

Google started the September 2026 spam update on 24 September 2026, globally and for all languages according to the Status Dashboard. The rise in the following days falls within the rollout period. That does not prove that the whole spike comes from the spam update.

The Sistrix status page has three entries from these weeks. On 27 August, Sistrix reported that Google was routing clicks through redirects such as google.com/goto, making data collection more complex. According to an addendum, processing was back to its usual rhythm on 1 September. On 16 September, data collection was running at a reduced rate after further changes at Google. And on 26 September, one day before the outlier, Sistrix wrote: “Google is currently returning incomplete or distorted search results in some cases.” New data for the Visibility Index would only be published after an additional quality check, and fewer keywords than usual would be updated each day. The Visibility Index and rankings would therefore show less movement than normal.

In the status notice of 26 September, Sistrix does not link it to the radar. Neither do I. The two are close in time. I cannot derive a causal link from the available information. Nor does this mean that the value is faulty. Sistrix writes that new data is only published after an additional quality check. But there are two questions I ask myself about every value from 26 September onwards: does the radar measure the same number of keywords here as before? And if fewer keywords are updated, do the low values of 29 and 30 September really show calm?

In my own Search Console (property seo-kreativ.de, search type Web), 27 September looks unremarkable: 9,923 impressions, against 8,218 on 26 September and 11,607 on 28 September. That is data from a single website. It is not comparable with the Sistrix index and can neither confirm nor rule out a broad movement in the search results. They only show that I see no impact on my site on that day.

Sources: Sistrix Google Update Radar and Semrush Knowledge Base, retrieved on 30 September 2026.

The same days in both tools, all values for Germany. The Semrush values come from the public Sensor view, not from a project-based Personal Score.

Sources: Sistrix Google Update Radar (tooltip values, Germany) and Semrush Sensor (public view, market Germany, all categories, desktop or mobile toggle, no Personal Score), both retrieved on the evening of 30 September 2026. The scales are not comparable, only the course over time is compared. Values for 30 September can change later that day.

Putting the numbers directly against each other makes no sense because of the different scales. The course over time does. Sistrix was elevated on 25 September, while Semrush mobile stood at 1.0 that day. From 26 September both tools show clearly more movement than before. After that they diverge: Sistrix drops to 1.17 on 29 September, Semrush desktop stays between 4.6 and 6.8 and reaches its highest value on 30 September.

There is also a difference that is easy to overlook. According to a notice in the tool, Semrush recalculated the baseline for all markets on 18 September 2026. From 26 September, Sistrix reports fewer updated keywords. So on these days both curves are based on data that is in the middle of changing. More on the Semrush side is in my article on the Semrush Sensor.

The “SERP Types” table lists the elements Sistrix records in the search results, with their share and a small trend curve. For Germany on 30 September 2026, images stood at 68.47%, AI Overview at 40.73%, Knowledge Panel at 26.54% and videos at 20.75%.

Two things are missing from the page. It does not say what the “change” column refers to. For “additional vertical sources” it shows a share of 4.28% and a change of -12.29%. That cannot be a difference in percentage points, otherwise the share would have been above 16% before. The display points more towards a relative change. Sistrix does not explain the reference value and period on the page. And it does not explain how the shares are counted. That is why I use the table as a hint as to which element is moving, not as a measurement.

1. Open the Google Search Status Dashboard. Confirmed updates are listed in the release history with their start date and, once complete, their duration. The overview on the Ask SISTRIX page on Google updates, by contrast, listed the March 2026 core update as its most recent 2026 entry on 30 September 2026, although the page shows an update date of 21 August 2026. The May 2026 core update and the spam updates of June and August are missing there.
2. Check the Sistrix status page. If Sistrix reports problems with data collection, read an outlier with caution.
3. Put a second tool next to it. For Germany the Semrush Sensor is a good choice because it shows desktop and mobile separately. If both tools rise on the same day, that is a stronger indication of a broad movement. Because of different keyword sets, devices and methods, it remains an indication.
4. Look at your own data. In Search Console, look at impressions and positions by day, device and page. How to narrow down a drop cleanly is in my guide on what to do when impressions collapse.
5. Wait until the update is done. While a rollout is running, the situation changes daily. Compare before and after only with some distance to the end.

Why I now read the tools’ status pages as well has to do with the end of the num=100 parameter in September 2025. Sistrix itself names num=100 on its status page as the biggest impact. Since then, Sistrix wrote there on 27 August 2026, Google has changed how search results are delivered almost every week. So I read a curve in a tool in the context of data collection. If Sistrix itself reports a reduced rate or additional checks, I compare individual daily values with particular caution.

For the German market, the Sistrix Update Radar offers a free 90-day history. That is its big advantage. Its limits are on the same page. It measures mobile only. The scale is relative, and Sistrix does not disclose its basis. And according to the Sistrix status page, data collection was running with restrictions in September 2026.

The value of 27 September 2026 shows why this matters. A 136 looks like an earthquake. In my own data there was nothing to see on that day, and the public Semrush Sensor for Germany was between 2.8 on mobile and 6.2 on desktop. Without a cross-check I would have made a completely different story out of it.