Texas Instruments TI-89 Titanium Graphing Calculator, Black

Excellent. My son is using this for Calculus.

Best product ever, Except that the batteries died after a month of usage. I am using eveready alkaline now and lasts more than a year under heavy usage. Also storing self created programs is not useful as the calculator resets some times without prior notice causing the user programs and past calculations to get erased. Does 3-D graphing very well though in that small lcd screen. Using the later colour models in not useful for me as their resolution is not any where near that of the modern phones. And I wouldn’t want to remember another device to hook up every three days to the power outlet. Besides the device will be useless once the rechargeable battery dies. This one though can run a lifetime if maintained properly as it uses disposable akaline batteries. And awesome for quick and dirty calculations when you don’t want a full fledged laptop.