Datenschutzerklärung · information according to Art. 13 GDPR · last updated October 2026
This website sets no cookies, uses no tracking or third-party analytics, and loads nothing from other websites: fonts, icons and the formula renderer are served from this server. The only personal data processed are the technical data that every web server receives (see Server logs). From these, after shortening the IP address and removing query strings and the details of the referring page, our server computes visit statistics (see Visit statistics).
Prof. Xhek Turkeshi, Institute for Theoretical Physics, University of Cologne, Zülpicher Str. 77, 50937 Cologne, Germany. Email: turkeshi[at]thp.uni-koeln.de
The website is hosted by DigitalOcean, LLC (New York, USA) on a server located in the United States. When you open a page, the web server automatically records in its log files: your IP address, date and time of the request, the requested address, the referring page, your browser's user-agent string, and the HTTP status of the response.
These data are needed to deliver the website and to keep it secure (for example to detect attacks), and in shortened form for the visit statistics described below. The legal basis is Art. 6(1)(f) GDPR; our legitimate interest is the secure and reliable operation of the website. The log files are deleted after 14 days at the latest. DigitalOcean processes these data on our behalf under a data processing agreement (Art. 28 GDPR); the transfer to the United States is based on the EU–US Data Privacy Framework and the EU Standard Contractual Clauses.
We count visits to this website from the server log files, without cookies, without scripts in the pages and without passing data to anyone. Once an hour, a program on our server reads the log files of the last 14 days and shortens every line before anything else happens: the IP address is cut to its network part (for IPv4 the last of its four numbers is set to 0, for IPv6 everything after the first 48 bits), the query part of the requested address is removed, of the referring page only the name of the website is kept, and all other fields except date and time, request method, requested address, protocol, status, response size and the browser's user-agent string are dropped; a referring website given as an IP address is left out. From these shortened lines the open-source program GoAccess computes, in the server's memory, totals for these 14 days: requests and visitors per day and hour, the pages and files requested, the referring websites, the HTTP status codes, and the countries, browsers and operating systems of the visitors. To count a visitor only once per day, it combines the shortened IP address with the user-agent string; this combination is not stored, and the shortened lines themselves exist only while the hourly run lasts.
What is stored is the resulting report with these totals, which is replaced every hour, and, for the long-term trend, two numbers per day: the number of visitors and of requests. These data contain no complete IP address and are not used to identify anyone; the daily numbers are deleted after at most two years. The country is looked up on our own server in the IP to Country Lite database by DB-IP (licensed under CC BY 4.0). The statistics are visible only to the site administrator.
The legal basis is Art. 6(1)(f) GDPR; our legitimate interest is to know how the website and the teaching material are used. The statistics use no cookies or scripts: nothing is stored in your browser, and only the data your browser sends with every request (IP address, requested address, referring page, user-agent) are evaluated on our server. In our view, consent under § 25 TDDDG is therefore not required. You can object at any time (Art. 21 GDPR) by writing to the address above; we then leave the IP addresses or network you tell us out of all future statistics.
The QuBite exercise pages save your progress (experience points, streak, completed lessons, the exercises you missed, and your settings) in the local storage of your own browser, under the key qubite:v1. These data never leave your device and are not sent to us or to anyone else. Storing them is strictly necessary for the function you use (§ 25(2) no. 2 TDDDG). You can delete them at any time with “Reset progress” in QuBite's settings or by clearing this website's data in your browser.
If you write to us, we use your address and message only to answer you (Art. 6(1)(b) or (f) GDPR) and delete them when they are no longer needed.
Links to other websites (for example LinkedIn, Google Scholar, arXiv, ORCID, journals, and the websites of the university and funders) are plain links. No data are transferred to these providers unless you click on a link; from then on, their privacy policies apply.
The administration area of this website uses a session cookie only for the login of the site administrator. Visitors never receive it.
You have the right to access (Art. 15 GDPR), rectification (Art. 16), erasure (Art. 17), restriction of processing (Art. 18), data portability (Art. 20), and to object to processing based on legitimate interests (Art. 21). To exercise them, write to the address above. You also have the right to lodge a complaint with a data protection supervisory authority, for example the Landesbeauftragte für Datenschutz und Informationsfreiheit Nordrhein-Westfalen.