Why is Scan Rate Measured in Hz, not Hz/s? Spectrometers have a specification called scan rate. As spectrometers measure spectrum, one would think the units of scan rate would be like Hz/s - meaning, the bandwidth scanned per unit time. Like if a spectrometer scanned 10 GHz in 100 ms, the scan rate would be $$\frac{10 \textrm{ GHz}}{100 \textrm{ ms}}= 100 \textrm{ GHz/s}$$ 
However, it seems as though scan rate is measured in Hz. For example, this commercial spectrometer has a 5 THz spectral range with a scan rate "up to 20 Hz". What does this mean exactly?
Another example is this paper where they say right in the abstract "At a scan rate of 9 kHz a time resolution of
230 fs is accomplished"
 A: Based on comments by @dmckee and @Farcher , it seems like the unstated assumption is that spectrometers always scan their entire available bandwidth.
So for the commercial spectrometer in the question with a 5 THz spectral range with a scan rate "up to 20 Hz", the scan rate is:
$$(5 \textrm{ THz})(20 \textrm{ Hz})=\frac{5 \textrm{ THz}}{0.05 \textrm{ s}}=100 \textrm{ THz/s}$$
One of the comments suggested using Hz$^2$ as a unit; seems sort of awkard; this would then be 100 THzHz, or 100 x 10$^{12}$ Hz$^2$ or even 100 MHz$^2$.
On a further note, another commercially available spectrometer calls it "Real-time data acquisition" instead of scan rate, with "10 spectra/s" meaning the entire bandwidth is scaned in 0.1 s.
A: The bandwidth of the spectrum is a red herring. Scan Rate refers to how fast the spectrum analyzer can generate a spectrum - ie the number of spectra per second. The limiting factor in this measurement is the discrete number of data points in the spectrum, not the continuous frequency bandwidth of the spectrum. 
So a scan rate of 20Hz means (for example) that the analyser can refresh the screen 20 times per second. This is useful if you are looking at changes in the spectrum on the time scale of 1s or more.
Saying that a bandwidth of 10GHz has been scanned in 100ms is meaningless for comparison purposes unless you also know the resolution of the scan. A spectrum analyser which can acquire 1000 data points from a spectrum which is a mere 1kHz wide in 0.1s is more powerful than one which takes the same time to acquire 100 data points from a spectrum 1THz wide.
Number of spectra is dimensionless so the unit of $Hz$ is correct. 
