Steroids and other medications. Long-term use of oral or injected corticosteroid medications, such as prednisone and cortisone, interferes with the bone-rebuilding process. Osteoporosis has also been associated with medications used to combat or prevent: Seizures; Gastric reflux; Cancer; Transplant rejection; Medical conditions
The main functions of using a compass are: 1  tell which direction you are traveling - your heading. 2  tell which direction an object is from you - its bearing. 3  keep you following a straight line of travel. 4  orient a map - aligning a map with the actual land.  triangulation - determining your location with a map.
The compass is showing you what direction the magnetic field is in, so you can use the right hand rule to work out whether the current is flowing north to south or south to north. There's a good diagram of the magnetic field around a wire here.