NiMn2O4 and substituted variations are the dominating materials for NTC-thermistors used for temperature sensors and inrush current limiters. Due to higher demands on the reliability of T sensors, the mayor challenge for further developments is the reduction of resistance drift, commonly associated with this type of NTC. This requires a fundamental understanding of these aging phenomena. Essential for the electrical properties is the cation distribution in this spinel system, which is still a matter of controversial discussion. We propose an unprecedented, complementary in-situ study, combining Seebeck measurements with NPD experiments to create a complete picture of the cation distribution in NiMn2O4, which will help to understand ageing phenomena and provide better approaches to avoid them. As NiMn2O4 is the basis for a wide range of NTC-materials, understanding it thoroughly is of great importance for many other related works and research aspirations.