Something for the prop guys here: both versions of the Imperial Code Cylinders (original Radiation Dosimeters) used in Star Wars by the Imperial officers. The blue cap version used by Grand Moff Tarkin, Cmdr. Praji and other officers, and the non-blue cap (the rarest one) used by Chief Bast and General Tagge. Finally I have 2 of each type - in fact I have 3 blue caps (maybe I'll sell my extra some day) and 2 others.
In the 1960’s a company by the name of RA Stephen & Company Ltd, England, UK, made Radiation Dosimeters, that would end up being the props used in Star Wars for the Imperial Officers. The ones used in Star Wars are called direct reading pocket ionization dosimeters. They were typically the size and shape of a fountain pin at that time.
Each dosimeter contains a small ionization chamber (approximately two milliliters). Inside each chamber is a central wire anode. Attached to the anode is a metal coated quartz fiber. These units can be positively charged so that the quartz fiber is attracted to the anode. When the unit encounters radiation, ionization occurs inside the chamber producing electrons.
These electrons are attracted to a positively charged anode, which reduces the net positive charge, allowing the quartz fiber to return to it’s original position. This movement can be calculated and is directly proportional to the amount of ionization (radiation).
BTW a nice difference in the color of the blue cap from my old and new dosimeters (the old one has a darker blue):
