This piece was custom built for me, and is pretty much as top of the line as replicas come. Where to begin!
First of all, in my opinion, this tricorder is as close to first generation as I could ever hope to find. It may very well be a first generation copy off the studio master. Pure speculation here, but its sheer size indicates that it's VERY high up on the generation chain. It is 100% legit, in the sense that there is no doubt in my mind that this is a replica of a studio piece, and not a well made fan piece. Not only have I had enough exposure to the real tricorder through pictures and other reference, but the source of these convinces me further that it is the real thing. It also matches the ones currently being sold by roddenberry.com. I should point out that the body of this tricorder is made of resin, just like the early mark VI tricorders made for the show. Of course, the paint job is spot on to the screen used ones. Good old Krylon Dove Grey (or whatever it's called today!) misted with a bit of silver.
The graphics are also just about as accurate in design as you could possibly hope. They are spectacular. The one difference is the production methods. These were printed onto photographic paper by an inkjet printer. The original graphics for the mark VI tricorders used in the different incarnations of trek were screen printed onto clear vinyl. Still, the minor change in production values doesn't take away from the overall quality.
This tricorder has a full electronics package, accurate to the screen used tricorders. It does not have any sound. It features a backlit view screen, the four chase LEDs on the Alpha-Gamma indicators, and a number of other lights and blinkies. Even more spectacular is the fact that the maker reproduced the "Spring open" functionality only found in the early tricorders. When you pull down the brass release latch on the side of the door, it swings open via a pulling mechanism inside the tricorder. Too frickin' cool! The maker of this tricorder indicated to me that he was still wrestling with replicating the ratchet sound that accompanies this opening door. If I recall correctly, it was this spring open mechanism that was originally responsible for creating the ratchet sound that was reproduced in later model tricorders in post production using sound effects.
As you can see from the pictures, this tricorder has the removable medical head and scanner. The med scanner is fully functional (in that the center red LED lights up when the button is pressed) and is held in place magnetically when placed into the medical head. The head itself is held into the tricorder using paint destroying ball-catches, the same methodology used in the tricorders created for the series. The science scanner is actually missing a detail, but is still very cool nonetheless. It features two flashing LEDs that turn on when the gold button is pressed, and turn off when it is pressed again. Very cool stuff!!
Historically speaking, this tricorder is the predecessor to the vacuum formed ones that were made by Ed Miarecki for later seasons of TNG. The Mark VI came in a number of varieties, some of which included a white "EMRG" well, where others had a black one. Like other tricorder, a 35mm slide was used for the display screen graphic. Mark VI tricorders also showed up in episodes of Voyager, though they were usually seen attached to the sides of biobeds.