Rechneronline in English Imprint & Privacy

About Me

This is me:

Jürgen Kummer
Buchenberg, Germany

E-Mail: juergen [at] jumk.de

Jürgen Kummer, 2015

The operator of rechneronline.de, author of the individual articles and programmer of the calculators. Photo from 2015.

• Born in Kempten, Germany, in the spring of 1972

• Graduated from high school in 1993 with advanced courses in mathematics and English; research paper on Julia sets and Mandelbrot set [German]

• From 1993 to 2006, I held various jobs (including as a programmer) and pursued studies (mathematics, psychology, computer science)

Sometime during this period, the internet emerged. I discovered it in 1998, and in 2000 I created my first websites, initially just for fun. I acquired skills in HTML, CSS, JavaScript, and PHP partly during my studies and partly, of course, on the internet (thanks to Selfhtml!). Soon, I was missing a few things on the internet that I could create myself. Specifically, websites where you could calculate something after entering values. My very first idea was to convert kilometers to miles, which is mathematically simple, but nobody wants to do it in their head. And, of course, there are many more such units to convert. The first calculator page was therefore in the year 2004 for converting units of length; other units soon followed. Conversion websites already existed, but the idea here, which I hadn't seen anywhere else before (which doesn't mean that it didn't already exist), was to enter one value and then convert it to all other units of that quantity simultaneously with a single click.
The realization that there was more to calculate than simple unit conversions was, of course, obvious. Over time, numerous other calculators were created. From the end of 2005 onward, I had a separate, new domain for these: rechneronline.de. Existing calculators on the old domain, however, remained there.
Around 2006, it became clear that I could make a living from this kind of work. I became self-employed and soon dropped out of my computer science studies, as only one of the two was viable. Initially as a sole proprietorship, then very quickly as a partnership (GbR) together with Sarah, my fellow student and a very good friend. This brought entirely new ideas and interests to my mathematical skills, ideas I would never have considered otherwise, and which could be perfectly translated into practical, everyday calculators. This contrasts sharply with my often more theoretical and abstract ideas. So, it was an excellent complement. Sadly, Sarah passed away in 2019. Since then, I've had to continue as a sole proprietorship again.
The focus of the site is therefore of course back on my topics in mathematics and natural sciences. For example, there are the calculators for geometric shapes. These started around 2006, first with the simplest shapes. However, the topic proved so fruitful that it has continued to be expanded even 20 years later and has now grown to well over 300 different geometry calculators. The total number of calculators across all topics amounts to several thousand, created over more than 20 years.

Besides these calculators, other websites have also been created. Firstly, as a related topic, a perpetual calendar that updates itself. Secondly, I'm fortunate enough to live in a beautiful and touristically interesting region, the Allgäu. This led to the Allgäu Travel Guide travel guide, which, along with Sarah, gave me the reason and opportunity to explore the region extensively. The inspiration here was, of course, reading Douglas Adams' Hitchhiker's Guide to the Galaxy multiple times. While exploring the galaxy wasn't possible, and even the Earth was too big for two people, our local area certainly allowed for a similar undertaking. Besides, creating calculators is a desk job, so a completely different website that gets you moving is a welcome change.

The goal of all my/our pages, especially the calculators, is to be helpful for a wide variety of applications. But of course, not all topics are equally important. In the author's opinion, the most important issue in the world right now is the environment and climate, because our lives and futures depend on it. Therefore, I gladly create calculators on these topics whenever the opportunity arises to make a meaningful contribution. Renewable energies and the necessary shift away from fossil fuels are particularly important here. Hence, for example, pages on photovoltaics and electromobility as future-oriented topics, in which I also personally undertake and report on projects, for example, with yield data from my photovoltaic systems.