I have worked as a designer and typesetter for over 15 years and “proofing” has always been very important. A few things that have been discovered is the words “THE, OF, A, AN” and other "non essential words can at times be “skipped” over when reading something. Sometimes this can lead to certain words being left out, etc. A person can swear that they have read over it a thousand times and yet still something can be left out. This is because our brain tends to “fill in the spaces” automatically and subconsciously that often we do not realize we do it.
Here is a prime example:
I cdnuolt blveiee that I cluod aulaclty uesdnatnrd what I was rdanieg. The phaonmneal pweor of the hmuan mnid, aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in what oredr the ltteers in a word are, the olny iprmoatnt tihng is that the first and last ltteer be in the rghit pclae. The rset can be a taotl mses and you can still raed it wouthit a porbelm. This is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the word as a wlohe. Amzanig huh ? Yaeh and I awlyas tghuhot slpeling was ipmorantt!So a tip I learned along time ago is if you have to proof something very important, word for word, and you want to make sure you have looked over everything then the failsafe way to proof spelling is
Backwards.
Yup. Sounds weird but it works.
Start with the last word and read just the word. Then the next to last word, etc. This keeps you from “reading” the words and makes you focus on the spelling of each individual word as a separate entity.
Of course this takes forever and something I would not recommend but if it is a vital sentence using custom words (Like words in a technical manual that may not appear in a computer spell checker’s dictionary) I would recommend backward reading.
On a side note this phenomenon can be attributed to drawing as well. A person tries to draw a person and ends up drawing something that has no resemblance in the end has suffered from their “left side” of their brain interfering with their “right Side”.
Solution: Take the picture you wish to draw and turn it upside down. Turn you paper upside down and draw what you see. The left side of your brain cannot “see” what the upside down picture is and becomes confused. The right side of your brain takes full control and tada! You just became a better reproduction artist!
Just thought I would share those tidbits while I was bored here at work 
Waht do you do for a lvniig?