This paper is in memory of Rob Milne. It recalls the scientific experience of the TIGER and TIGER SHEBA European projects that he led through the presentation of CA∼EN, a model-based diagnosis software that was devised during the projects and integrated with the commercial tool TIGER^TM. Several lines of more recent work that all build on CA∼EN are also presented. These developments are closely related to the Qualitative Reasoning and Model Based Diagnosis communities, represented by the MONET network of Excellence in Europe. Their theories inspired this work and I like to believe that this work inspired the communities in return. Rob Milne and myself were active members of MONET.