The new "Snapshots" system in Spectral Workbench brings the ability to maintain different versions of a spectrum for different uses. This feature [is being planned in Github](https://github.com/publiclab/spectral-workbench/issues/192) and will be coming online by January 2016.

##What are Snapshots?

Snapshots freeze a specific state of your spectrum so that the data at that moment can be used in other contexts. It's like version control for your data -- if you use a spectrum by reference, such as to calibrate or in a comparison, you can expect that you'll see the snapshot of that spectrum just as it was when you made that reference. No later changes to the spectrum will affect referring work. 

##When are they created?

Certain operations cause snapshots to be created automatically, so that a "frozen" version of the spectrum is permanently available for that operation's use. These include:

* referring to a spectrum with certain powertags, including the `calibrate:`, `subtract:`, `transform:`, `range:`, `crossSection:` and `smooth:` powertags

We hope to make the flip operation also trigger snapshotting; [progress can be seen here](https://github.com/publiclab/spectral-workbench/issues/237).

##Why are they necessary?

Snapshots ensure that if you rely on a spectrum for any of the operations above, any subsequent changes to that spectrum do not (by default) affect your reference to that spectrum. Your reference is to the snapshot, not the spectrum, and nobody besides you can modify that data. So if you use one spectrum over and over, for example as a calibration reference, or as a baseline to subtract with, you'll always be accessing the same data. If you change the referred-to spectrum later, you'll be able to manually update the reference to a more up-to-date snapshot. But this won't happen automatically.