Figure 7-45.  Continuous flow mask and rebreather bag.  Figure 7-46.  EDS-011 portable pulse-demand oxygen system.  Figure 7-47.  Onyx pulse oximeter.  7-39  systems are to be serviced. Oxygen system servicing should  be accomplished only when the aircraft is located outside  of the hangars. Personal cleanliness and good housekeeping  are imperative when working with oxygen. Oxygen under  pressure creates spontaneous results when brought in contact  with petroleum products. Service people should be certain to  wash dirt, oil, and grease (including lip salves and hair oil)  from their hands before working around oxygen equipment. It  is also essential that clothing and tools are free of oil, grease,  A pulse oximeter is a device that measures the amount of  oxygen in an individual’s blood, in addition to heart rate.  This non-invasive device measures the color changes that  red blood cells undergo when they become saturated with  oxygen. By transmitting a special light beam through a  fingertip to evaluate the color of the red cells, a pulse  oximeter can calculate the degree of oxygen saturation  within one percent of directly measured blood oxygen.  Because of their portability and speed, pulse oximeters are  very useful for pilots operating in nonpressurized aircraft  above 12,500 feet where supplemental oxygen is required.  A pulse oximeter permits crewmembers and passengers of  an aircraft to evaluate their actual need for supplemental  oxygen.  [Figure 7-47]  breathing cycle because oxygen is only delivered during  inhalation. Compared to continuous-flow systems, the pulse- demand method of oxygen delivery can reduce the amount  of oxygen needed by 50–85 percent. Most pulse-demand  oxygen systems also incorporate an internal barometer  that automatically compensates for changes in altitude by  increasing the amount of oxygen delivered for each pulse as  altitude is increased.  [Figure 7-46]  Pulse Oximeters  Servicing of Oxygen Systems  Before servicing any aircraft with oxygen, consult the  specific aircraft service manual to determine the type of  equipment required and procedures to be used. Certain  precautions should be observed whenever aircraft oxygen 