For more information online, see "History of PTR and PTB," PTB, https://www.ptb.de/cms/en/about-us-career/about-us/history-of-ptr-and-ptb.html (accessed 06/17/2015)
A detailed history of the formation and first years of the PTR is
David Cahan, An Institute for an Empire: The Psysikalisch-Technische Reichsanstalt, 1871-1918. (Cambridge, Cambridge University Press, 1989).