Barcol hardness test the Barcol impressor was developed by Walter Colman as a hand-held, portable means of assessing the hardness of a material during World War II. The United States Army Air Corps required a hand-held method of checking the hardness of rivets due to concerns that aircraft could be sabotaged by replacing normal rivets with soft lead or wooden ones which would fail during flight. The impressor operates when the tip is pressed against the material in question. The hardness of the material determines how far the tip indents and this is transferred by a tension spring and lever to be read
Walter Janka called upon to testify against Janka, with the words: Wolfgang Harich had already been convicted, and sentenced to a ten-year jail term in March 1957, in respect of the same alleged conspiracy as Janka. The two had previously worked together at the Aufbau publishing house. Harich was brought into the July show-trial by as a leading prosecution witness: his testimony now heavily implicated Janka. The two former friends would remain estranged from one another for the rest of their lives. Janka served the first part of his sentence in Berlin-Hohenschönhausen prison where he had been held on remand, but in