I didn't find it on my legitimate visit to Calcelmo's Laboratory and Dwemer Museum, but heard that it was another item to make the Thieves Guild happy. So I went back - and cannot find it. The wiki article is even bugged since the link to the lab and museum both go to the introduction page about the Understone Keep. Any help here?

It is in the labaratory, along the wall to your right as you face the door that leads out in to the balcony. Hope this helps.

It won't be there if you're not on the Thieves quest

AHA! Thank you. It's been really bugging me and I've been searching for a hour or two.

Sure it will I forgot to grab it my first time through and went back a 2nd time and it was sitting there took it and took off. Gave it to Delvin and it now sits on my nightstand in Honeyside.