Add a comment here:
```
# c0 is the reference value, in angstroms.  c1 is the reference *pixel* corresponding to c0
```
Is this true, though?  Maybe I misunderstand.... I would've thought `c1=0.0`.

And perhaps below:
```
# the flux pixels have indices 0,1,2,3... which are translated to physical units using the WCS
```
```