lowlight, when you say manual, do you you mean doing each equation individually or the parameters need to be set manually? As far as the reason, I find it prudent to have backups when possible. Plus calculators are fairly resilient, simple (software wise) and have the ability to swap an SD cards to other units while costing less.
I can always learn to make a program for a calculator, but if one is made and available or convertible, that would be preferred.