A friend of mine is an avid collector, and much more experienced with a much deeper collection. Occasionally he throws out a nugget of experience that I often find helpful. Usually it is something obvious to a more experienced collector, but not always to me, a novice. He shared one with me that I thought was very helpful, and extremely obvious I know, but here it is for those like me. When viewing a coin through a loop, always turn the coin upside-down when you first look at it. You will pick up abnormalities, DDRs, RMM, doubling, etc., much faster that if you looked at the coin right ways up. He mentioned that the brain often fills in details on familiar objects during a quick look, and you may miss something if you are in a hurry. I went trough a few random coins in my collection using this technique, and although I did not find anything interesting, I did see the coin in a new light. I am definitely going to keep this in mind next time I am out coin shopping.
Although I wouldn't agree with that comment 100%, I would agree that you do see the coin in a different light when it us upside down....more to come on this comment later in the message. When using a loupe to look at a coin, it should be looked at from as many different angles as possible and under different intensities/types of light. I have three lighting sources at my desk, one halogen, one incandescent and the other is florescent. You would be surprised on what you see under each type of lighting spectrum. Also, I can adjust the intensity of my florescent lighting and halogen lighting. The coin should be held appropriately between your fore finger and thumb and rotated and tilted accordingly to open the surface of the coin to different angles of lighting. This is what will enable you to really see any surface defects and mint mark variations. In getting back to your comment about holding the coin upside down, I would like to mention that this is a good exercise to get the mind to see the coin the same way as if you were holding it right side up. What I mean by this is that our minds our programmed to read something one way...in this case with the coin right side up. Turning the coin so that the bust is upside down shouldn't change the surface or how we see the coin, but our minds tell us differently. Many times when looking for varieties and such, I will do personal exercises and grab coins off the table and look at them as I hold them in my hand no matter what the rotation is. I try to train my brain to see the coin the same no matter how I hold it. It is more difficult than it seems. Try this when you get a chance. There are some coins that I can pick up and look at no matter how they are looking back at me and have the same results if the coin was orientated in the bust upright position and then there are other coins which mess with my mind and I can only look at them one way.
Look at them from all angles - not just right side up or upside down. You will notice different things - like scratches or hairlines. I always rotate the coin with the naked eye - obverse and reverse. Doing this sometimes you can even eliminate some coins from going under the glass. Then do the same under the glass. If you like the coin set it to the side or let the dealer hold it separate. Then look some more - then before buying look at it again carefully. I do this at the coins I look at in person. At the local shop I might even go over to their books, bring one back, attribute the coin - before deciding to buy. Overkill on some coins I know I want - but I have found hidden hairlines or scratches that made me eliminate a coin for consideration. Just my opinion.
I've heard things similar to the upside down rule. A teacher told me when spell checking you should read the sentence backwards to avoid just reading and not spellchecking
