You'll notice that many spectra on [Spectral Workbench](https://spectralworkbench.org) have a scale showing "nm" or nanometer units on the horizontal axis. To get scaled data, you must calibrate your spectrometer. There are several kinds of calibration but here we're talking about **wavelength calibration**, which allows your spectrometer to display a wavelength value for any color of light it sees. Luckily, this is easy.
1) Find a **fluorescent light bulb** -- preferably a compact fluorescent bulb you can put your spectrometer very close to. Point your spectrometer at the bulb -- if it's too bright, point it at a piece of white paper or wall which is brightly illuminated by the bulb.
 
2) You'll see an image like the above example; if you're on a computer, it may appear horizontally. The lines you see are from mercury in the bulb, and since we know what wavelengths they **should** be, we can use this to calibrate your device.
Save this spectrum, and tag it "fluorescent" and/or "CFL". Now you'll need to use the analysis tool to calibrate; it will walk you through the process.
###Calibrating using your fluorescent bulb spectrum###
You can calibrate your spectra or your spectrometer because the spectrum of a compact fluorescent light bulb is well known. Two lines in particular are very stable and easy to recognize:
* **Mercury 2 line:** "middle blue line" at 435.833 nanometers
* **Mercury 3 line:** "bright green line" at 546.074 nanometers
Click the **Calibrate** button and you'll be guided through identifying and clicking on each of these lines. Once you've calibrated a single spectrum, you'll be able to apply that calibration to all of the spectra you collected with that instrument.
Watch this video for a walkthrough of the whole process:
##Known issues##
There is still a bug in the code that can cause odd calibration results -- Jeff needs to fix it (sorry!). Try pressing "re-extract" than after it clears the previous calibration, clicking "calibrate" again and following the instructions once more. Try comparing your calibration to another (search for "CFL calibration").
##Custom calibrations##
You can calibrate a spectrum with 2 known pixel positions and corresponding wavelength values with the following URL format:
> https://spectralworkbench.org/spectrums/calibrate/SPECTRUM_ID?x1=242&w1=554&x2=483&w2=780
Where SPECTRUM_ID is the ID of your spectrum, x1 and x2 are the pixel locations, and w1 and w2 are the wavelengths for those positions.
