Technological accuracy
I believe the series is set between 1850 and 1870. Are there any historical errors about the technology and products that are seen in the show?
Alternatively, have you been surprised by some of the technology seen in the show, but later found out that it was actually available to people at the time?
I was a bit skeptical when I saw the episode about the hot air balloon (in season 2, I believe), and there were pipes pumping gas into it that seemed pretty modern.
Also, in "Devil on her shoulder", you see power lines. I was surprised at first, but then I thought that it probably must be correct, since they had telegrams which after all had to travel through wires.