These weapons were state of the art technology for their time. Although historians knew crossbows were used, until the discovery of the terracotta army there was no evidence as to how effective or how advanced they were. The crossbows found in the pits were extremely advanced and greater than any other crossbow invented at the time. The locking mechanism found was new technology and was casted in bronze.  This locking mechanism was one of four bronze pieces of the crossbow that were casted. Casting multiple parts for a weapon is an action that required great precision so they would properly fit together. However the Qin Dynasty was able to produce bronze work with such precision that the tolerance for error is within a fraction of a millimeter.  Along with the crossbows themselves, the most common item found in the pits were crossbow bolts. Over forty thousand crossbow arrows were found in the burial pits. After measuring over 1,600 arrows, researchers concluded that each arrow had such a small difference in measurement that they are considered systematically identical to one another.  This is another example of the impressive and remarkable power of the Qin Dynasty production.
Although the quality and precision of the weapons were impressive, the most impressive aspect of the weapons is the state that they are in today. Despite having been buried for around two thousand years the swords are clean, shiny, lacking corrosion, and are still lethal today. After undergoing chemical analysis scientists discovered that there is an anti-corrosion layer on the weapons. This layer is a dense oxide layer and may mean that Qin factories were using chrome on the surface of their weapons. This method of metal preservation was not discovered by Europeans until centuries later in the 1930s. 
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- Weapon Formation Map