undocumented change to ISIS IS extinction calculation

[Robin Leadbeater]

There appears to have been a change in the way ISIS calculates Interstellar extinction somewhere between versions 5.9.3 and 6.0.3. See http://www.spectro-aras.com/forum/viewt ... 284#p17284

Does anyone have a reference to the formulae ISIS has used ?

Also are earlier versions of ISIS still available on line somewhere?
They used to be at this link but it no longer works
http://www.astrosurf.com/buil/isis/download/

Thanks
Robin