Not to pipe in and start up discussion again... but I'm in the court with the .001 answer here's why: This was an inferance question... and you could not infer that before the invention of SQUIDS that measurements that small were unattainable. With regard to the .001 answer : some kind of experiment has to be done to establish that measurement! Hence, that answer makes more sense.
At least to me.
I tend to agree with what's being said there on that other topic: Everybody brings what they remember and hence some of their bias to the boards... so who knows