As a complement to the "indicator-frame" here is the references of the cited
book :
The inventor is Dr Julius Paschke
The book : "Der Neue Baurahmenimker" by Maria E. Paschke (1952)
French edition : "Le cadre-temoin", J.Mosbeux, Bruxelles, ed. (1973)
I don't know if an english edition was published.
Regards. Jean-Marie.