An old mirror goes round robin
In one of the many corners of the optics lab (yes, really, there are more than four!) lies an old, but not forgotten mirror from the good old days of BESSY-I. While it is well worn from years of reflecting synchrotron light, it is far from obsolete. In fact, as Frank Siewert points out, it is still very useful.
As part of their work on metrology, many labs regularly check the performance of their instruments in a so called Round Robin comparison, where they measure the same sample (mirror) with different measurement machines around the world and compare the results.
For those tests, they need well-defined samples – and so mirrors like the old BESSY I-mirror get to travel the world quite a bit. Unfortunately, Frank Siewert says, he usually has to stay at home.