This Exactra 19 was part of the Exactra series that was manufactured by Texas Instruments though you wouldn't know it by looking at the front of the calculator. For some reasons, possibly marketing, TI decided to place their only identifying mark on the back cover in small lettering. The Exactra series included the 19, 20, 21, 22and 23 models and was produced starting in 1974. The Exactra 19 is one of the cheaper options in the series and only had 6 digit display.
The Exactra 19 uses 3 AA batteries as opposed to a 9v and has no external power supply as its more expensive brothers the 21 and 22 do. The Exactras aren't exactly rare and I've seen prices all over the place. One sold for $9.99 in good working condition while others have sold for over $100.
This is a very rare Sanyo ICC-808D calculator. As you can see it utilizes nixie tubes (gas discharge tubes) for the display. It uses algebraic logic, has 4 functions and 18 keys. It was made in 1972 and has a level of popularity based not upon its calculating abilities nor its retro design. No, it has a large following because of its use in the movie Ghostbusters. In early shootings of the movie the characters had what they is called a "belt gizmo" which just happened to be made from Sanyo ICC-808D circuit boards. Basically it looks like they took the top and bottom covers off and used what remained for the gizmo that hung from their belts.
So, given the fact the two groups of collectors show interest in the calculator, its price is correspondingly high and its supply low. The Sanyo ICC-808D's are pretty hard to find and usually sell for around $500+ when they become available. There are also people that recreate the circuit boards for those that wish to create an authentic ghostbusters costume.
It is a neat looking calculator and definitely belongs in any calculator collection but you may find it difficult to get your hands on one. Even the non-functioning units are highly priced due to the fact that the Ghostbusters fans don't really care whether the calculator works or not.
This is the TI Concept II calculator. It was sold by a discount department store called Zayre's in the mid 70's and is basically a re-badged TI-1250. In fact, it's exactly the same except for the colors on the faceplate. It was introduced by Zayre in 1976 and retailed for about $17.00. It has a 8 digit red LED stick display, one memory register and ran on a 9 volt battery. It uses algebraic logic with 6 functions and 24 keys.
The Concept series from Zayre included the Concept 10, Concept 24, Concept I, Concept II, and Concept III. The Concept 24 was made by Lloyd's while the latter three were made by Texas Instruments. The TI Concept II is not a real popular calculator with collectors but does have some novelty and was made by TI so it does have its place in a collection. The Concept II calculator will sell for $25-$70 depending upon condition and accessories. The Concept III is probably more rare and will sell for over $100.00.