Erinnerung an Hans Dennert

Vorgetragen von IJzebrand Schuitema auf dem IM2004


Today we have been presented a series of lectures on the many activities and manufacturing aspects of the ARISTO firm in the last decades of its active existence. All presentations had as subject a specific own theme related to the history of manufacture of slide rules.


These historical facts and data are for us as collectors an important addition of knowledge to our hobby. I think I can make the conclusion that all of us have been enriched in our knowledge on the ARISTO firm.

But, what is not expressed sufficiently is the history of the person who shaped this firm and who had to care for all activities and decisions to attain the wanted and obtained results: Mr. Hans Dennert. I will try to sketch a portrait of him in my lecture and tell about aspects which are probably unknown or perhaps unexpected among us as collectors.

As all slide rule manufacturing firms have been through, the use of the slide rule stopped in the 1970’s due to the pocket calculator coming to the market. Consequently manufacture came to an end. The ARISTO firm had a good name among all who used a slide rule which resulted in the highest sale ever made in 1974.

The father of Mr. Hans Dennert, Mr. Georg Dennert, born in 1900, was in spite of his high age very active in the firm until 1979, to help and assist his son Mr. Hans Dennert to run the firm. Altogether it could not anticipate the decline of sales after 1974. In the year 1976 only 27% of the former high production quantity could be put on the market. One can understand that this was a very big disappointment for both of them, having been such a flourishing firm during so many years. Trying to set up an other line of production for other kinds of instruments was not successful. The geodetic instruments however were a good selling object. One of these was the „Koordinatograph“. And it was especially this instrument in which the ROTRING firm was interested to put it on their sale list under the original ARISTO name. Negotiations between ROTRING and ARISTO resulted in the sale of the whole ARISTO plant and production facilities, and the taking over of part of the labor to ROTRING. Doing it this way the ARISTO name remained.

The taking over was considered to be a positive decision. But we can imagine that it was a hard time for Mr. Hans Dennert. A good running firm, your life-work, with such a good name, coming to an end of your personal influence, that will leave behind traces.

In discussions with his wife Mrs. Irene Dennert, with whom I talked several times on these backgrounds, she told me how all this went by, socially and personally. Having had intensive and close contacts with his business relations during the years of prosperity, these contacts suddenly came to an end. His private circle of friends had always been less important in his daily life because of his business duties.

All this hold, more or less, that he could not invest time in personal contacts with friends. His firm was on the first place. This made him a lonely person in this last and very problematic period of his firm. The second half of the seventies, in which he decided to sell the whole ARISTO firm, have been for him very difficult years. His sons were too young in those days to be of any help and assistance for their father.

It is not astonishing that he was left in a feeling of disappointment after he had sold his firm to ROTRING. There was hardly one to talk with on his disappointment. His business contacts were not the right sound-board and a circle of friends too small to find a good response. Let us try to imagine what were his feelings at that moment. You have invested all your energy all your life, with success, into a well running firm, and than suddenly this accumulation of troubles without any sound-board.

We do not know Mr. Dennert as a person like this. We know him as the beloved person who has enriched the world of collectors of slide rules with his knowledge and with items from his remaining stock of slide rules. It is interesting to analyze this revolution in his doings. It will strengthen us, hearing all this, in our notion that we have to do with a very particular personality. I feel privileged to may report on this to-day in this final lecture. The data used come from several visits to Mrs. Dennert, talking about her husband, and from personal contacts with Mr. Dennert since the end of the 1980’s until his death in 2000, and from his many activities in coordination with him and other collectors. Maybe a psychologist could write a good story, comparing the period before and after 1988, periods so totally different for one and the same person.

The beginning of this is more or less at the moment of my first visit to him. I came back from a holiday abroad and crossed Hamburg. My slide rule hobby had in those days already a rather size in numbers of items and results of historical research. Especially this historical research was an important part of my hobby. This made me decide to visit the ARISTO firm in Hamburg, hoping to be able to talk with one or more workers of the slide rule department on several aspects of design and manufacture of slide rules. I went to the lady in the reception and put my question. Alas she had to disappoint me. Before having sold the ARISTO firm to ROTRING the slide rule department had stopped manufacturing and no worker of the active slide rule manufacturing period was in service anymore. She immediately followed proposing to contact Mr. Dennert, the last owner and managing director of ARISTO, because he knew all I wanted to be informed on. I supposed I could not ask him for such a contact. But she insisted to contact him, because Mr. Dennert was a nice gentleman who would appreciate a contact like this, and took the telephone, called him, and made an appointment for the next day.

This visit to him was very pleasant and instructive for me, but also for him as I heard years later from Mrs. Dennert, and made a change in his personal attitude to the slide rule. It was for him the first time that a non-businessman was making contact with him on the subject of his personal knowledge on the slide rule in all its aspects, like design and application, related to collecting. Preparing this contact, Mr. Dennert had organized a small exhibition of special slide rules in his room and many photo’s, books, manuals and documents related to the history of his firm. And Mrs. Dennert had been busy preparing delicious cakes etc. to the tea. It was a very animated afternoon during which Mr. Dennert informed me on many aspects and activities of his former managerial period. In reverse I could tell him a lot on my experiences and on the activities of other collectors known to me. I went back home with some very interesting acquirements for my collection and a few books and documents with valuable information.

In the following years I could inform him on the activities of the Dutch collectors group, called „Circle“, and on the „Oughtred Society“ in the USA. This resulted into his membership of the „Oughtred Society“ in 1993 and of the „Circle“ in 1995. And especially these memberships caused an important revolution in his attitude to the slide rule and all related aspects, and not as a result of manufacture and sale, but as intermediate of contacts with friends focused on collecting. The memberships of the „Oughtred Society“ and the „Circle“, and later his contacts with the German collector’s circle „R.S.T.“, and with the English collectors, opened for him a totally new world of friends. And for all those friends a new relation with whom it was nice and instructive to cooperate in one or another form due to his charming personality and his large knowledge on all slide rule aspects. Mr. Dennert wrote several articles, published in the magazines of the collector’s circles, all enlarging the knowledge of the slide rule collectors on aspects they had only little knowledge whatsoever.

The Dutch „Circle“ decided, in close cooperation with the „Oughtred Society“ and the English collectors circle to organize the first international European slide rule collector’s meeting, IM-1995. It was Mr. Dennert who prepared and presented an important contribution. He gave an extensive insight in the coding and dating system of the ARISTO slide rules. This information was used later by Herman van Herwijnen in his catalogue of slide rules, the so-called „Blue Book“, later transformed into a CD.ROM. Thanks to Mr. Dennert’s contribution there are no secrets anymore on the used capitals and numbers on the backside of the bodies of the slide rules, and we are enriched by an overview of all types of slide rules manufactured by ARISTO.

His lecture was especially interesting for all participants because it was an owner/manager/director of a slide rule firm himself – absolutely unique – who presented it and who was a participant like all others. Next to this lecture he brought a small selection of slide rules with him as an exhibition. And as a surprise he surprised all participants with a gift of 5 different slide rules, especially manufactured many years ago for the South American market and never been available for sale in Europe.

Many participants had a private contact with Mr. Dennert during this IM-1995. One of them was our youngest member, Thomas van der Zijden, who just had started as a student on the Technical University Delft in chemical engineering. Mr. Dennert and Thomas have been sitting at a table long time, Mr. Dennert explaining Thomas background of scales and use of the ARISTO chemical disc Nr.630, System Bückle.

Mr. and Mrs. Dennert were hosted in the Maliehotel quite near to our conference house. Our member Nanco Bordewijk heard of their plans to spend a couple of days extra in Amsterdam. Nanco, living in the center of Amsterdam, immediately offered them to stay in his house for some days instead of looking for a hotel. It happened as such and they had two days an interesting contact, Nanco showing them his huge collection of technical and constructional puzzles of which both were very impressed.

The Saturday after the Friday conference the participants visited the collector’s fair in the Jaarbeurs in Utrecht. I had a large showstand with part of my collection. That showstand was meeting point for all our conference participants. A journalist entered my stand and wanted to have an interview with me. I proposed to him not to interview me but Mr. Dennert, because it might be a unique opportunity for that journalist to talk with a former owner/director of a slide rule firm. That journalist and Mr. Dennert talked with each other for a long time. This was also for Mr. Dennert a particular aspect of his new circle of contacts.

Once, after having started his membership of the „Oughtred Society“, Mr. Dennert and his wife visited relatives in the USA and Canada and combined these visits with meetings with Bob Otnes and Rodger Shepherd. These contacts were followed by close contacts in later years in Germany.

Mr. Dennert took part in the IM-1996 in Cambridge. The German collectors circle started preparing IM-1997 and Mr. Dennert joined the organizing committee. Part of his contribution was preparing the ARISTO exhibition, representing the period PVC was used as material, 1935 and after. As a base for that exhibition my theme collection was used to which Mr. Dennert added missing items. Extensive oral and written consult on what to exhibit and in which way and added by what kind of explanatory text between him and me resulted in an exhibition mounted on 15 showpanels size 60/120cm, altogether a wall length of 9 m. Among these many items there were several very unique and rare ones. His participation in IM’s stopped in 1998 in Huttwill, Switzerland.

In 1986/1988, Mr. Dennert also spent energy to the exhibiting of slide rules in the „Deutsches Museum“ in München. In 1994 he donated part of his documents and remaining stock of items to the new founded „Museum der Arbeit“ in Hamburg and made a documented description of this donated collection of slide rules.

The intensive contacts in collector’s circles as mentioned before resulted in many personal contacts. And these personal contacts were so different compared to his contacts of former years with businessmen. It gave him much pleasure and satisfaction. But unless all these new and changed contacts, he always remained „Mr. Dennert“. When we joined a meeting or a contact and were dressed in sport shirts or sweater, he was always dressed in jacket. This was part of his past and was continued in the present. I do not think there was anyone who called him „Hans“. In this context it is funny to mention that even Mrs. Dennert, when she speaks about her husband, she doesn’t say „my husband“ or „Hans“, but that she always calls him „Hans Dennert“, adding his family name to his first name. When I asked her some month ago how this happened, she started laughing and told me that it found its origin in the period he was active as manager in his firm, during which all people called him „Mr. Dennert“ and that she, as a kind of respect to him, forgot to call him in an intimate way „Hans“, but „Hans Dennert“. When she explained and grew conscious of this, we both have laughed hearty. Since, we both never talk about him else than „Hans“.

At the end of 1999 (November) his health grew worse. It resulted in a frequent stay in hospital and diminishing activities in slide rule aspects. Finally he died in October 2000. We lost a very likable personality who enriched us with much knowledge on many aspects of our fascinating hobby and who entered an other world in which stress caused by business responsibility changed into relaxation by contacts with friends. The funeral was very impressive. I am happy to have had the opportunity to be present at that ceremony. May he rest in peace.

The memorial book being available from today on is a dignified expression of respect to him. We have to be very grateful to our German collector friends for their initiative and activity for compiling and publishing.

As concluding remark I want to express my appreciation – probably the appreciation of all of you – that Mrs. Dennert, our Irene, has continued the activities of her Hans Dennert in such a particular way, that we are still able to consult the ARISTO archive, and that she even puts energy in lectures, as she has done in IM-2001 and now in IM-2004, to enrich us with more knowledge on Hans Dennert’s ARISTO firm.

Dear Irene, our kindest thanks for all you did for us.


IJzebrand Schuitema