Combine the chopped onions, olive oil, garlic, cumin, oregano, chiles, cider vinegar, and salt in a blender or food processor. Blend the ingredients together at medium to high speed until a thick puree forms. Do not drain the adobo sauce from the chipotle chiles before adding them. You should pour the sauce into the blender along with the chiles. Spread the sauce into the bottom of your slow cooker. Place the beef on top of it, and pour the beef broth over the meat. Place the bay leaf on top. Coat the beef in the sauce by turning it a few times, dipping all sides in the sauce at least once in the process. Use a 5-qt to 7-qt (5-L to 7-L) slow cooker for best results. Cut the beef into several chunks, if necessary, to fit it into the slow cooker. If you want it done sooner, set the slow cooker to high and cook the beef for 6 hours. Resist the temptation to open the lid and peek at your meal as it cooks. Doing so releases the trapped steam, and that steam is partially responsible for cooking the meat. As a result, the overall cooking time can increase 15 to 30 minutes every time you open the slow cooker. Remove the beef from the slow cooker and place it on a cutting board or rimmed baking sheet. Use two forks to shred the beef into pieces, working from the outside in. While shredding the beef, you should also discard any fat. A rimmed baking sheet or cutting board works best since some of the juices inside the beef can run as you work with it. Without a rimmed surface, these juices can create a big mess. Transfer the shredded beef to a large bowl. Ladle a little of the cooking liquid into the bowl, mixing after each addition. Add enough sauce to keep the beef thoroughly moist, but do not add so much that the beef drown in it or becomes soupy. If you have some cooking liquid left behind after you coat the beef, you can fill a spare ice cube tray with it and freeze the liquid for later use. These cubes of barbacoa sauce can be used to flavor stocks, soups, gravies, and other dishes later on. If you are not ready to serve the barbacoa yet, return it to the slow cooker and switch the appliance to its "warm" setting. You can keep it warm using this method for another 2 to 4 hours. After that point, you should consider transferring any uneaten beef to airtight containers and storing it in the refrigerator. Reheat it in the microwave after refrigerator storage. The beef barbacoa is ready to eat. Serve it to your family or guests while still warm, and offer it with an accompaniment of tortillas, onion, cilantro, and salsa.
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One-sentence summary -- Puree the sauce ingredients. Layer the sauce, beef, and broth in the slow cooker. Cover and cook on low for 8 to 10 hours. Shred the beef. Mix the shredded beef with the barbacoa sauce. Keep it warm in the slow cooker. Serve.

Fax machines are often shared by offices or several people within an office. Since anyone can see a fax sent to a fax machine, it is a good idea to include a cover letter. This will ensure that your fax gets to the correct person. The cover letter includes information like the recipient's name, the content of the fax, and how many pages it includes. It should also include the sender's information, such as name and fax number, so that the recipient will know whom it came from and can reply if necessary. Next, you will need to dial the fax number, just the same way you would on a telephone. On most new fax machines, the area code will not need to be dialed for a local number but is still necessary for long distance numbers. Some fax machines require the area code regardless of location. Check or ask about your machine. The country code (the number 1 for US phones and fax numbers) will also sometimes need to be dialed before local numbers but only when the area code is also required. The country code is almost always necessary to dial long distance numbers. You will often also need to dial 9 before dialing long distance numbers. Check the specifications for or ask about your individual fax machine. Be sure that the number you are using is the fax number and not the phone number of the person you are trying to reach. Often the numbers will be listed next to each other on business cards and it is easy to misread it or look at the wrong number. When you put the materials to be faxed into the machine, you will need to put them in in the appropriate direction. The paper will be scanned, so if the paper is facing the wrong way only the back side will be scanned and the fax you send will be blank. Ensure that the papers a facing the right side up before sending the fax. Different fax machines feed in different ways. Helpfully, all fax machines are labeled with the appropriate direction to place the papers. Somewhere near the area where you feed the paper, look for a symbol of a sheet of paper with a corner folded down. You will see on this symbol that one side of the sheet has lines and the other side is blank. If the folded down corner has the lines, this mean the sheets must be fed into the fax machine with the blank side facing you. If the folded corner is blank, this means you must feed the machine with the front side of the paper facing you. Fax machines work best with standard size paper. Sending anything in a non-standard size may not work or it may jam or harm your fax machine. If you need to send something of a non-standard size, such as a receipt copy, you will want to make a photocopy of the item first and fax the photocopy instead. The most common size paper for fax machines, as with printers, is A4 or American letterhead.
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One-sentence summary -- Create the cover letter. Dial the fax number. Determine the feeding method. Fax the right material.

If you notice chest pains, nausea, dizziness, irregular heartbeat, or shortness of breath while exercising, stop immediately. The exercise may be straining your heart. Call your doctor or 911 if the symptoms do not disappear quickly. If you have a prescription for nitroglycerin, then carry it with you during exercise. You should also write down the symptoms you experienced, the time of day, when you last ate, how long they lasted, and how often these symptoms appear. Speak with your doctor about any other symptoms before continuing an exercise program. The doctor may want to perform another stress test before you resume exercising. Wear the correct clothing and shoes for the type of exercise you are doing. Stay hydrated during exercise and be sure that someone knows where you are going when you leave to workout outside. Always use good judgement and stay within your limits. It is much better to continue to work out each day at an intensity you feel is lighter than you can manage, rather than to be sidelined for weeks with an injury or be re-hospitalized with another cardiac event. In very cold or hot weather your body has to work harder to provide oxygen to your cells, including your heart. Do not exercise outdoors if the weather is colder than 35F (1.7C) or hotter than 85F (29.4C) with humidity greater than 80%.
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One-sentence summary --
Look for signs that your heart is working too hard. Prevent injuries and accidents. Avoid exercising outdoors when temperatures are high or low.