I do not think it is worth just getting a pda for electronics calulations as eventually u will be able to do them on a calculator (remembering the forumlas)
But there are things like this:
**broken link removed** - Electronics Bible - like a glossary of terms, contains over 35,000 entries
**broken link removed** - Electronics Calculator
I think a PDA is a great investment. I use mine for taking lecutre notes, games, mp3 player, diary, web browsing, calculator etc. etc. But as i said, when u get better at electronics u will remember the formulas and will not need a PDA to do things!