In one sentence, describe what the following article is about: You may be able to figure out which program you're supposed to use to open the file based on where the file is stored or what the file is named. For example, if you found the DAT file inside of an "Adobe" folder, you can guess that an Adobe app is meant to open the DAT file. If the file is inside of a folder that contains other system files for your computer, it's probably best to leave the DAT file aloneit's probably used by your computer's built-in programs or features. If you received the DAT file as an email message or from a download site, try contacting the person who sent or uploaded the DAT file and asking what program they used to create the file. This is unlikely to yield much if you're asking on a crowded forum or a file-sharing site, but you should be able to get an answer out of a coworker or a friend via email. You may be able to use your computer's built-in text editor to view some (or all) of the DAT file's contents: Windows Open Notepad, then drag-and-drop the DAT file into the Notepad window. Mac Open TextEdit from your Mac's "Applications" folder, then drag-and-drop the DAT file into the TextEdit window. Depending on the DAT file, you may be able to see a line or two of text that determines the type of software used to open the file. Even if you don't see a line about the specific program you need to use, you might find a line that indicates the type of file (e.g., video or text) that the DAT contents are meant to be. Some programssuch as VLC Media Player, iTunes, Preview, and Notepad++can be used to open a large number of file types without changing the files' contents. For example, VLC Media Player can open most video file extensions, while you can download and use Notepad++ on Windows to open virtually any text-based file. Unfortunately, if you haven't been able to determine the DAT file's origin program by this point, you'll have to start attempting to open the DAT file with different programs on your computer. You can do this by opening a program, dragging the DAT file onto the program's window, dropping it there, and waiting for the file to open. If the file opens in a recognizable format, you've found the correct program. If the program displays the DAT file as an incomprehensible jumble of characters or refuses to open the file, your selected program isn't the right program.
Summary: Consider the context of the file. Ask the file's creator. Open the DAT file in a text editor. Look for information about the DAT file. Try opening the DAT file in a general program. Use trial-and-error.

Molar mass is the mass (in grams) of one mole of a substance. Using the atomic mass of an element and multiplying it by the conversion factor grams per mole (g/mol), you can calculate the molar mass of that element. An element's relative atomic mass is the average mass, in atomic units, of a sample of all its isotopes. This information can be found on the periodic table of elements. Locate the element and find the number underneath the symbol for the element. It will not be a whole number, but will have decimals. For example, for hydrogen, the relative atomic mass is 1.007; for carbon, it is 12.0107; for oxygen, it is 15.9994; and for chlorine, it is 35.453. This is defined as 0.001 kilogram per mole, or 1 gram per mole. This converts atomic units to grams per mole, making the molar mass of hydrogen 1.007 grams per mole, of carbon 12.0107 grams per mole, of oxygen 15.9994 grams per mole, and of chlorine 35.453 grams per mole. Some elements are only found in molecules of 2 atoms or more. This means that if you want to find the molar mass of elements that are composed of 2 atoms, such as hydrogen, oxygen, and chlorine, then you'll have to find their relative atomic masses. Multiply them by the molar mass constant, and then multiply the result by 2. For H2: 1.007 x 2 = 2.014 grams per mole; for O2: 15.9994 x 2 = 31.9988 grams per mole; and for Cl2: 35.453 x 2 = 70.096 grams per mole. One mnemonic device for remembering diatomic elements (molecules of 2 atoms) is: Have No Fear Of Ice Cold Beverages (Hydrogen, Nitrogen, Fluorine, Oxygen, Iodine, Chlorine, Bromine).
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One-sentence summary -- Understand molar mass. Find the relative atomic mass of the element. Multiply the relative atomic mass by the molar mass constant.

Problem: Article: The makeshift watch compass described in this article uses the position of the sun in the sky to determine North and South. Because the sun is in a different part of the sky in the Northern Hemisphere (the part of the earth north of the equator) than it is in the Southern Hemisphere (the part of the earth south of the equator), it's important to account for this difference to ensure your compass is accurate. It's usually easy to tell whether you're in the Northern or Southern Hemisphere simply by virtue of knowing what country you're in (for instance, The Southern Hemisphere includes most of South America, Sub-Saharan Africa, and Australia). If you're at home (or otherwise near civilization), use a map, a globe, or an online geographical resource to find your position relative to the equator. If you're truly lost - for instance, in a life raft in the middle of the ocean, you may not have access to maps, encyclopedias, or the internet. Luckily, if you're deep in the wilderness and you don't know which hemisphere you're in, you can still determine whether you're in the Northern or Southern hemisphere by searching for Polaris, the North Star, in the night sky. This star is visible from the Northern Hemisphere, but if you're even slightly below the equator in the Southern Hemisphere, you won't be able to to see it. Note that the watch compass described in this article works best in the Autumn and Spring and can be inaccurate near the equator.
Summary:
Use a map to find your hemisphere at home. Use the North Star to find your hemisphere in the wilderness.