Purchased for my high school junior's chemistry class.  Texas Instruments is a reliable brand, the price was very good, and delivery was fast.  It's too complex for me, but I still go looking for the sine, cosine and tangent tables in the back of trig books if my kid asks me for help.  Oh, well, at least I can figure out the 4 basic functions on this, and the boy assures me it works well.