Thanks Rob and Paul.
Here's the spectra around Fraunhofer C (Ha) and E as they are at present. I'm not so confident of the dispersion ATM. If its right the sodium doublet should be visible in the RHS of the Fraunhofer E spectrum
and while I was working on the Fraunhofer D spectrum last night 0.9214 A/pixel wasn't making much sense, so I tried calibrating off the two sodium lines... and that suggests a dispersion of about 0.5 A.pixel!
hmm... more work to do
.
Al.