A spell-check function is useful for catching misspelled words, typos, and accidental repetitions (the the) in your papers. But be careful. The checker won't signal a word that is actually a word, even if it isn't the one you intended — for example, when you inadvertently type form for from. Spell-checking also doesn't distinguish between homonyms, so if you have trouble with its and it's, it won't help you. Consider the spell-checker as an aid, not a replacement for your own careful proofreading.
