This thesis was originally motivated by a curiosity about how historicity and culture forms understanding in activities in a work situation. I wanted to gather and structure some thoughts about what happens when scientific, formally educated, knowledge, which dominates in a traditional desk learning situation, is facing knowledge which is learned through practice in real work situations with complex technology. These contradictions, I believe, must be something we all experience every day, more or less consciously. A study could perhaps be done at any kind of activity or work. I chose a dialysis department and the work of dialysis nurses as an example. This turned out to be a good choice, since these two perspectives of understanding becomes quite clear in a setting with new technology, which, together with routines and treatment, is developing and changing constantly. Patients, nurses, doctors, patient wards, dialysis machines, water cleansing system, and so forth create a complex system. It is not possible to analyse this system, or even create anything meaningful for it, unless bringing in a perspective of time and culture, into the discussion. Historicity explains and forms work practice at the very same time, when the nurses have to create a standpoint and an understanding for the actions they have to take. Creating meaningful design into complex environments is not helped by aiming for a total understanding of the whole system. Instead, agents that form the change of understanding, behaviour and action may work as keys into the creation of new design.