Q: An expected value is usually found on tests and school labs. Basically, this is the most precise, common measurement to come up with, usually for common equations or reactions. You can compare your own results to get Absolute Error, which measures how far off you were from the expected results. To do so, simply subtract the measured value from the expected one. Even if the result is negative, make it positive. This is your absolute error!  Example: You want to know how accurately you estimate distances by pacing them off. You pace from one tree to another and estimate that they're 18 feet apart. This is the experimental value. Then you come back with a long measuring tape to measure the exact distance, finding out that the trees are in fact 20 feet (6 meters) apart. That is the "real" value. Your absolute error is 20 - 18 = 2 feet (60.96 centimeters). For example, if you're measuring something with a meter stick, the smallest unit marked on the meter stick is 1 millimeter (mm). So you know that your measurement is accurate to within + or - 1 mm; your absolute error is 1 mm. This works for any measurement system. Many scientific tools, like precision droppers and measurement equipment, often has absolute error labeled on the sides as "+/- ____ " Say your Absolute Error was "2 meters." This tells your viewers exactly how far off your error was. But if you write that your error was simply "2," this doesn't tell your audience anything. Use the same unites as the ones in your measurements. The best way to learn how to calculate error is to go ahead and calculate it. Take a stab at the following problems, then highlight the space after the colon (:) to see your answer.  Jill is studying chemical reactions. After mixing and matching, her test tube contains 32 grams of substrate. The accepted value for her experiment was 34 grams. Her Absolute Error is: +/- 2 grams  Clive is testing reactions in chemistry. It takes 10ml drops of water to cause a reaction, but his dropper claims it is "+/- .5ml." The Absolute Error in his measurements must be: +/- .5ml No scientific study is ever perfectly error free -- even Nobel Prize winning papers and discoveries have a margin or error attached. Still, understanding where error comes from is essential to help try and prevent it:  Human error is the most common. This is from bad measurements, faulty premises, or mistakes in the lab. Incidental energy/material loss, such as the little fluid left in the beaker after pouring, changes in temperature due to the environment, etc. Imperfect equipment used either for measurement or studies, such as very small, precise measurements or burners that provide uneven heat.
A: When given an expected value, subtract the value you got from the expected value to get the Absolute Error. Alternatively, when measuring something, assume the absolute error to be the smallest unit of measurement at your disposal. Always add the appropriate units. Practice with several examples. Understand what causes error, and how you can work to eliminate it.

Q: Go to Amazon’s Seller Central site to sign up for a third party seller account. Fill out the registration form with your name, email address, and unique login password. Once your account has been activated, you’ll be able to sell your used items on Amazon. You may also be asked to provide some basic financial information, such as your debit card or bank account number. From your Amazon seller account, highlight the “Inventory” tab at the top of the page and click the option to “Add a Product.” Enter the bar code found on the back of the DVD to generate a unique listing for the item. You can also search for the DVD by title and select it from a list. When searching by title, be sure to choose the correct version of the item. If you’re selling a copy of The Matrix, for instance, you’ll want to specify whether it’s the standard theatrical version or 2-disc Special Edition. You'll be given a few different options to choose from, including “New,” “Used - Good,” and “Used - Acceptable.” Click the option that most accurately describes the item you’re selling so that potential buyers will have an idea of what to expect.  A basic condition designation should be enough to paint a picture of an item that doesn't show any real wear and tear. Amazon has a very particular set of quality standards for the used items sold through their site. Make sure your DVDs meet the guidelines outlined in the "Help" section of the Amazon Seller Central website. After specifying a basic condition, make a note of any additional features that the seller might want to know about. This is a good chance to report examples of minor damage or incomplete packaging, such as “missing insert booklet” or “small crack near corner of case.” Be as specific as you want—buyers tend to appreciate transparency. Be honest about the condition of your DVDs. If you try to pass them off as better than they are, there’s a chance they could be rejected by Amazon’s Fulfillment specialists or reported by a disgruntled buyer. Try to come up with a number that reflects what the item is worth and is fair for both you and the buyer. For a brand new DVD that’s still in the packaging, you may be able to make back most of what you paid for it. Used titles, especially those that show wear and tear, are usually sold for a smaller percentage of the original purchase price.  If you’re not sure how to price your items, take a look at similar listings and aim to match the average asking price.  Keep in mind that the value of DVDs is steadily decreasing as they’re phased out and replaced by other formats like Blu-Ray and streaming video. Buyers may go with another seller if they think you’re asking too much.
A:
Register for an Amazon seller account. Create a listing for the DVD you want to sell. Select the item's condition from the options provided. Give a detailed description of the item's condition. Set a price for your listing.