The TI-30Xa Solar is the most useful, directly and intuitively useful calculator that I have ever used from Texas Instruments. As a 'klutz' for complex procedures with calculators, I need a calculating device that will give me the answers I need without much recourse to the (quite loseable) instruction pamphlet. This calculator will provide you the right answers in a way no more complex than a basic understanding of (American) high school math would instruct.
I like the fact that the 'Solar' has a larger decimal-place than the battery operated TI-30Xa. As a person with far-sightedness, I need that decimal to be big enough to stand out when I need to copy down the answer. The battery-model has a really tiny decimal place which with my presbyopia is too too too much to see, one needs a magnifier to find out whether one has 236 or .236...Not so with the big decimal on the Solar model.