As a respiratory therapist (RRT) I have a need to know the oxygen level of the people I am working with on a regular basis.  It is necessary for their health and my future that I be able to take accurate measurements.  To do this I do as so many of my colleagues do and use a Fingertip Pulse Oximeter.  It allows me to see the exact level of their oxygen when we are doing our therapy sessions so that I will know if their oxygen is getting to low for their safety.  I recommend that all RRTs carry an affordable light weight one.