App Privacy Policy

DCZT built Kalku for the Google Play Store and App Store. DCZT is the trade name under which I, an individual developer in the Czech Republic, publish my apps. Kalku is free to download and has no in-app purchases or subscriptions.

This page is used to inform visitors regarding my policies with the collection, use, and disclosure of Personal Information if anyone decides to use my Service.

The Personal Information that I collect is used for providing and improving the Service, as described below. I will not use or share your information with anyone except as described in this Privacy Policy.

The terms used in this Privacy Policy have the same meanings as in the Terms of Use, unless otherwise defined in this Privacy Policy.

Who is responsible for your data

The controller of your personal data under the EU General Data Protection Regulation (GDPR) is DCZT, an individual developer in the Czech Republic, support@dczt.dev. I am not required to appoint a data protection officer; for anything about your data, write to me at that address.

Information Collection and Use

Kalku does not ask you to create an account. Apart from the usage statistics described under "Analytics", I do not store personal data about you on servers. What you create in the app stays on your device (see "Data stored on your device" below).

Kalku contains no third-party code that collects data: no advertising, no third-party analytics and no tracking. The only third party involved is the store you downloaded it from:

• Apple App Store - App platform
• Google Play - App platform

Analytics

Kalku sends anonymous usage statistics to AnalyticsInsights, an analytics service I run myself on servers I rent from Hetzner Online GmbH in Germany and Finland (EU). Hetzner hosts the server and its backups for me and does not use the data for anything else; no other company receives it. The statistics carry no identifier for you, your device or your copy of the app: not your advertising identifier, and no random installation identifier either. Each time you use the app it makes up a random session number, which it keeps only in its memory and forgets when it closes, so the events of one visit can be grouped together but one visit cannot be linked to the next. The statistics are: your device model, operating system version, app version, language and time zone; your country, looked up from your IP address, which is then discarded and never stored; when you open and close the app and for how long; which screens and calculators you open and from where (the calculator library, search, favourites or recently used), which construction keys you press and when the display shows an error, whether a result is a plain number, a length, an area, a volume or a weight, how many characters a search had and how many results it found (never what you searched for), when you copy, save, share, rename, delete, reset or favourite something and how many lines it had, when you first move a 3D preview or a chart, the settings you change and the links you open from Settings, and your unit system, app language and visual style; and error reports, including the crash reports described below. Everything is encrypted in transit. I use this only to understand how the app is used, to fix errors and to improve it; I do not use it to show you ads, and I do not sell it.

If the app crashes, stops responding (an "ANR" on Android) or freezes (a "hang" on iOS), or Android closes it because your device ran low on memory, the app sends a report about it to AnalyticsInsights, usually the next time you open it. A report says what kind of problem it was and when it happened, and contains the error message and the technical stack trace (the parts of the app's code that were running; for an ANR, those of all the app's threads), together with the device and app details listed above. Email addresses, user names in file paths and app folder identifiers are removed from error messages and reports when they arrive.

Because nothing is stored on your device to identify you, Kalku does not ask for your consent first: the statistics are on when you install it, and you can turn them off at any time with "Share anonymous usage data" in the app's Settings, under Privacy. Turning them off stops all statistics and crash reports and deletes those still waiting on your device to be sent. What was sent before cannot be traced back to your device, so there is nothing that could be picked out and deleted. The legal basis is my legitimate interest in keeping the app working and improving it.

To help me read these statistics I may use an AI assistant (Claude, by Anthropic), which acts as my service provider. It works with the statistics described above, mostly as totals.

Nothing you type is ever part of the statistics: not the numbers you enter, not your searches, and not the names or notes of saved calculations. Only fixed values and counts are sent.

Purchases

Kalku has no in-app purchases or subscriptions, and it never asks for payment details.

Data stored on your device

Everything you enter or save in the app - your settings and stored sizes, the values in the calculators, your favourites and recently used calculators, and the calculations you save with their names and notes - is stored only on your device and is not uploaded to me. If you choose to share something from the app, it is handed to the app you pick through your device's share function and leaves your device only then. Deleting the app deletes the copy on your device, and I cannot restore it.

Backups

Your settings and saved calculations are included in your device's own backup if you use one: iCloud Backup or a computer backup on iPhone and iPad, and Google's backup on Android. That backup belongs to your Apple or Google account, and I cannot see it. Nothing to do with the usage statistics is kept in it.

Permissions

Kalku does not ask for access to your camera, photos, microphone, location, contacts, calendar or notifications. It uses the internet only for the usage statistics and crash reports described above; every calculation is done on your device and works without a connection.

When you share a calculation as a PDF or as text, the app hands it to the app you choose through your device's share sheet. Links in the app's settings (the privacy policy, the terms of use, and support by email) open in your browser or your email app.

Log Data

When something goes wrong in the app, it sends the error and crash reports described under "Analytics" to AnalyticsInsights, my own analytics server. They contain the device and app details listed there, but never your IP address. If you have allowed your device to share analytics with app developers, Apple and Google may also share anonymous crash reports and usage statistics with me; you can change this in your device's privacy settings.

Cookies

The app does not use cookies or any similar identifiers.

Service Providers

Some companies process personal data on my behalf, as my service providers (processors), and may use it only to provide their service to me: Hetzner Online GmbH, which hosts my own servers in the EU; Anthropic, whose AI assistant I may use to read the statistics; and Vercel, which hosts this website.

Legal bases

Under the GDPR, I rely on these legal bases:

• Performance of a contract (Article 6(1)(b) GDPR): to provide the features you use, and to answer you when you contact me.
• Legitimate interests (Article 6(1)(f) GDPR): to keep the app and my servers secure and working, to prevent abuse, to fix errors, to understand how the app is used, and to run this website. You can object to this processing at any time (see "Your Rights").
• Legal obligations (Article 6(1)(c) GDPR): where I must keep or disclose information by law, for example for accounting or in response to a lawful request from an authority.

Permissions you give on your device, such as access to the camera, photos, microphone or notifications, are your choice. The features that need them work only while you allow them, and you can withdraw them at any time in your device's settings.

How long data is kept

• Data in the app stays on your device until you delete it or delete the app.
• Usage statistics and error reports carry no identifier, and are kept for as long as they help me improve the app.
• Emails you send me are kept for as long as I need them to deal with your request and any follow-up, and are then deleted. Bug reports and feature requests sent with the form on dczt.dev are deleted after 24 months, and newsletter addresses are kept until you unsubscribe.

International transfers

My own servers are in the EU, at Hetzner in Germany and Finland. Some of the services described in this policy are based outside the European Economic Area, mainly in the United States - for example Vercel, which hosts this website. Where personal data is transferred outside the European Economic Area, the transfer relies on an adequacy decision of the European Commission (such as the EU-U.S. Data Privacy Framework, for companies certified under it) or on the European Commission's standard contractual clauses, as described in each company's own privacy policy. You can ask me for more information about these safeguards.

Security

I value your trust in providing me your Personal Information, thus I am striving to use commercially acceptable means of protecting it. But remember that no method of transmission over the internet, or method of electronic storage is 100% secure and reliable, and I cannot guarantee its absolute security.

Responsible Disclosure Policy

We take the security of our systems and data seriously. If you believe you have discovered a vulnerability, please follow these guidelines:

1. Do not exploit the vulnerability beyond what is necessary to confirm its existence.
2. Do not access, modify, or delete data that does not belong to you.
3. Report the issue to the website owner with details so we can reproduce the finding.
4. We will acknowledge receipt and work to address the issue as quickly as possible.
5. Testing is only authorized within the scope of this policy. Any testing outside of scope may be considered unauthorized and could be subject to legal action.
6. To the extent permitted by law, we are not responsible for any damage, loss, or impact to your devices, systems, or data at any time, whether or not it is related to security testing.

Links to Other Sites

This Service may contain links to other sites. If you click on a third-party link, you will be directed to that site. Note that these external sites are not operated by me. Therefore, I strongly advise you to review the Privacy Policy of these websites. I have no control over and assume no responsibility for the content, privacy policies, or practices of any third-party sites or services.

This website

The website this policy is published on is hosted by Vercel, which processes standard server logs (such as your IP address, browser and the page requested) to deliver and protect the site. I count visits with AnalyticsInsights, an analytics tool I run myself on my own server at Hetzner in Germany. It does not use cookies or store anything in your browser, follow you across other websites or store your IP address. Your IP address is used only for a moment: to look up your country, and, together with your browser's identification and a random value that is replaced every day, to count you as one visitor for that day, so visits on different days cannot be linked and your IP address cannot be recovered. It records the page visited, the referring site, your browser, operating system, device type and country, clicks on links and buttons (such as the store buttons, links to other pages and the FAQ), how long a page stays open, how far down it is scrolled and how quickly it loads. To help me read these statistics I may use an AI assistant (Claude, by Anthropic), which acts as my service provider.

If you send a bug report or feature request with the form on dczt.dev, your message, the app, platform and reason you choose, and your email address if you give one are sent to AnalyticsInsights on the same server, with the page you sent it from and your browser, operating system, device type, language and country (looked up from your IP address, which is not stored). I use them only to look into what you wrote and, if you left your email address, to reply. They are deleted after 24 months, or sooner if you ask me.

If you sign up for the newsletter, the only thing I ask for is your email address. It is sent to and stored by Brevo, the service I use to send the newsletter, and is used for nothing else. Every email has an unsubscribe link, and you can unsubscribe at any time.

The free calculators on this website run entirely in your browser, and there is no account. The numbers you type stay in the page and, once you change something, in its address so that a link reopens the same calculation. The visit counter is sent that address but keeps only its path, never the numbers in it.

Children's Privacy

These Services do not address anyone under the age of 13. I do not knowingly collect personal information from children under 13, and the apps never ask for an email address or other contact details. If you are a parent or guardian and believe that your child has provided personal information, please contact me at support@dczt.dev so that I can have it deleted.

Your Rights and Data Deletion

Under the GDPR, and depending on where you live, you have the right to access the personal data held about you and get a copy of it, to have it corrected or deleted, to restrict its processing, to receive it in a portable format, to object to processing based on legitimate interests, and to withdraw your consent at any time without affecting what was done before. I do not make decisions about you based solely on automated processing that have legal or similarly significant effects on you. I answer requests within one month.

Kalku has no accounts, and the usage statistics on my server carry no identifier, so nothing there can be traced back to you or your device, and there is nothing I could find to give you a copy of or to delete. You can stop them being sent at any time with "Share anonymous usage data" in the app's Settings, under Privacy. The data the app keeps on your device is deleted when you delete the app.

To have your email address removed from the newsletter, use the unsubscribe link in any email or write to me. You also have the right to lodge a complaint with a data protection supervisory authority, in particular in the EU country where you live or work or where you think your rights were infringed. In the Czech Republic this is the Office for Personal Data Protection (Úřad pro ochranu osobních údajů, Pplk. Sochora 27, 170 00 Prague 7, uoou.gov.cz).

Changes to This Privacy Policy

I may update this Privacy Policy from time to time, for example when an app gains a feature or starts using a new service, so please review this page periodically. The date below shows the current version. If a change significantly affects how your data is used, I will tell you in the app or on this page before it applies and, where the law requires it, ask for your consent again.

This policy is effective as of 2026-11-13

Contact Us

If you have any questions or suggestions about my Privacy Policy, do not hesitate to contact me at support@dczt.dev.