Joining the Delta Link tool is a very handy AST 5408 service light reset tool. I've never used one -- or seen one -- so I can't comment on particulars, but in roughly two weeks this little gem will be available to borrow.
It resets the Service light on 850s.
It's being donated to the program by a wishes-to-be-anonymous MVS member. I've thanked him in private correspondence, of course. Things like this make me so proud to run this site.
Help keep MVS on the web -> click sponsors' links here on MVS when you buy from them.
Also -> Amazon link. Click that when you go to buy something on Amazon and MVS gets a cut!