This is my main calculator that I use (I have two) and this has the most functions I have seen on a calculator. It has a total of 23 functions, but I don't think it includes functions for negative numbers. This calculator is very good for high school and college students because of its versatility and functions. Just make sure you keep the instruction booklet! Speaking from experience, this can be a life saver!
The battery life is pretty long and I think mine holds up fo about 15 min., so it lasts very long for a calculator. The instruction booklet gives detailed instructions on how to replace batteries for it. Just make sure to recycle the old batteries. So this is another reason it is very important not to throw away the instructions.
This calculator has technical support and hardware service.
I have had this calculator for about 7 years, so this has lasted longer than any other calculator I've owned.
This calculator is about the size of a candy bar so it may not be exact for a purse, but it carries in a back pack perfectly. It is expensive but I think you are mostly paying for the functions and a quality calculator. Because this calculator is indeed quality.