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 new PDS (party), but he soon became disappointed with this, and quit. Walter Janka died in March 1994 in Kleinmachnow and is buried there in the Waldfriedhof (Cemetery in the woods). Walter Janka Walter Janka (born in Chemnitz 29 April 1914, died in Kleinmachnow 17 March 1994) was a German communist, political activist and writer who became a publisher. Janka is notable for having spent time incarcerated as a political prisoner under the rule of the Nazis and later imprisoned under suspicion of counter-revolutionary activities by the Supreme Court of East Germany, in both cases serving most of his sentence