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.