Cosmological observations to shed light on possible variations - expectations, limitations and status quo

Cosmology contributes a good deal to the investigation of variation of fundamental physical constants. High resolution data is available and allows for detailed analysis over cosmological distances and a multitude of methods were developed. The raised demand for precision requires a deep understanding of the limiting errors involved. The achievable accuracy is under debate and current observing proposals max out the capabilities of todays technology. The question for self-consistency in data analysis and effective techniques to handle unknown systematic errors is of increasing importance. An analysis based on independent data sets is put forward and alternative approaches for some of the steps involved are introduced.