Red and Blue shift

It depends on your tool...

 

The spectrograph gives you signal over a range of wavelengths, so you should see characteristic peaks on a graph.

393 nm/392 nm = 0.26% which seems nicely in the range 0.1-1%.

 

There are a number of factors that determine the frequency range over which you will measure a spectral line:

http://www-star.st-and.ac.uk/~kw25/teaching/nebulae/lecture08_linewidths.pdf

 

Those spectrographs are looking at light that was emitted from an object. The spectral lines are absorbed at the SOURCE, not the instrument. In other words, the line at 393 nm absorbed by calcium is a result of actual calcium in the star or galaxy absorbing the light, not calcium here on Earth. The light that is at 392 nm is NOT being absorbed by calcium, the line is wider than 1 nm because of several different effects, such as the rotation of the star. (Part of the star is moving away and part is moving towards us, so the line is wider than it would be otherwise) When we look at the patterns of lines in the spectrum and compare it with our own lines here on Earth we see a difference where the lines are shifted to the red end, aka redshifted. Measuring the difference between the lines we observe from the object and our comparison here in the lab we can tell how fast something is moving away from or towards us.

 

As a minor curiosity, an isolated lab test has apparently demonstrated that electron density (of intervening media?) may play some role in the story of spectral line shift phenomena.
http://www.sciencedirect.com/science/article/pii/S0030402608000089

Respectfully submitted,
Steve