The metal fragment is identified as being from more than 400 years in the future using a "quantum dating" device. I will proceed with the presumption that quantum dating works like carbon dating; one measures the presence of a certain unusual, unstable object (such as a Carbon-14 atom) with the understanding that its absence its transformation into another object (such as a Carbon-12 atom). If this is how quantum dating works, then one of these two is true: 1) Time travel does not affect the state of the quantum particle. If this is the case, Archer's scan wouldn't work. 2) Time travel does affect the state of the quantum particle. If this is the case, VERY bad things would have happened to Archer when Daniels transported him to the 31st century.