Proofreading is an important phase of the writing process. Careful proofreaders check for errors in spelling, grammar, punctuation, names, numbers, and formatting. When checking spelling, do not rely too heavily on your computer’s spell checker.'

a. This selection is correct without any revisions.
b. This selection contains one spelling error and one comma error.
c. This selection contains one spelling error and two comma errors.

This selection is correct without revision. The first sentence is a simple sentence with one independent clause. Potentially someone might consider the word ‘proofreading’to be a spelling error, but this is a common compound word, hence it is no longer hyphenated. The second sentence is a simple sentence too. It includes a list, which is properly punctuated with commas. In American English, writers tend to do away with the comma before ánd’, but in proper British English, this is generally not the case. The final sentence is a complex sentence. The subject is understood to be ‘you’, although it is not stated explicitly. One might consider the word ‘formatting’to be misspelt. The common rule is that if there is a double letter, the vowel sound is preceding it is short, while a single consonant between vowels produces a long vowel sound.