Halmeter A/F 30 gauge, New in Box

[DOOMID]

Halmeter a/f gauge brand new in box, supposed to be one of the best and most accurate.

asking $100 shipped

www.halmeter.com <-----picture and specs here

[drwn kix]

Would this require an additional oxygen sensor or does it work off of the stock one? If it does require one, does it come with it and does it require welding in a bung to mount it? :?