The greater the number of interfaces in a process automation system, the higher the level of complexity. That may sound like a platitude, but it can result in quite a lot of unexpected requirements in a real-world application. This relates not just to technical issues but also, in particular, to communication with the respective product partners. The project in the Lithuanian city of Kaunas, which ProLeiT AG was commissioned to implement by the German plant manufacturer Pentair Südmo, is an excellent example in this context.