Privacy and cookies on Calculus
Here you can see what information Calculus processes when you use the site, and which cookies the site uses.
Who is responsible
Tom Frank Christensen is the data controller for Calculus.dk. You can write to kontakt@tomc.dk.
What you enter in the calculators
The calculators run on the server. When you fill in a field or press Calculate, the values are sent to calculus.dk, which sends the result back. The fields and the result are stored in your session, so the site can show them again if you reload or come back. The session is linked to a cookie in your browser and not to your name.
The session expires 14 days after your last visit and is then deleted from the server. If you delete cookies for calculus.dk in your browser, the site can no longer find your saved fields.
The solar panel calculators fetch production figures from the European Commission's PVGIS service. The server only sends the chosen city's coordinates and the system's data, not information about you.
The currency converter and the currency choice use rates from the European Central Bank and ExchangeRate-API. The server fetches the rates once a day and sends no information about you.
Server log files
Calculus.dk is hosted on a server at Hetzner Online GmbH in Germany. The web server records each request with the IP address, time, the page requested, response code, referring page and the browser's identification. The log is used for operations, troubleshooting and security. It is rotated every day, and each day's log is deleted after 52 days.
When you write to us
If you write to kontakt@tomc.dk, the email and the information you send are used to answer your message and possibly correct errors on the site. The email is stored with Proton (ProtonMail) and kept until Tom deletes it.
Statistics with Google Analytics
Calculus.dk uses Google Analytics to see how many people visit the site and which pages are used. This only happens if you choose Accept in the cookie choice. Before you have chosen, Google Analytics is not loaded.
If you accept, your browser fetches Google Analytics from Google and sets two cookies. Google states that Google Analytics 4 does not log or store IP addresses. The visit statistics are kept for 14 months. If you decline, Google Analytics is not loaded, and any Analytics cookies are deleted.
Cookies and local storage
| Name | Purpose | Lifetime | Requires consent |
|---|---|---|---|
| calculus-session | Remembers your inputs and results | 14 days | No, necessary |
| XSRF-TOKEN | Protects against forged requests | 14 days | No, necessary |
| _ga | Google Analytics: distinguishes between visitors | 2 years | Yes |
| _ga_ followed by an id | Google Analytics: remembers the state of the visit | 2 years | Yes |
| consent (local storage) | Remembers your choice about statistics | Until you delete your browser data | No, necessary |
| theme (local storage) | Remembers light or dark theme if you change it | Until you delete your browser data | No, only stored when you change theme |
| currency | Remembers the currency you have chosen in the calculators | 1 year | No, only stored when you choose a currency |
Who receives information
Hetzner Online GmbH runs the server where the site, the sessions and the log files are stored. Proton AG in Switzerland runs the email for kontakt@tomc.dk. If you accept statistics, Google receives the information from Google Analytics. Google may transfer information to the USA. Google LLC is certified under the EU-U.S. Data Privacy Framework.
Legal basis and your rights
Calculator inputs, the session and the server log files are processed because it is necessary to provide and run the site securely (legitimate interest, Article 6(1)(f) of the General Data Protection Regulation). Messages are processed to be able to answer you (same basis). Statistics with Google Analytics only happen with your consent (Article 6(1)(a) and the Danish cookie order).
You have the right to access the information about you and to have it corrected or deleted. You can also object to the processing or have it restricted. Write to kontakt@tomc.dk. If you are dissatisfied, you can complain to the Danish Data Protection Agency, Datatilsynet.
Change your cookie choice
Press the Cookies button at the bottom of the page to open the choice again. If you choose Decline, you withdraw your consent: Google Analytics stops, and Analytics cookies are deleted.
Updated
Last changed October 16, 2026. Also read About Calculus, or contact Tom.