A typical sensor will have an infrared LED 110 of wavelength 940 nanometers and a red LED  120 of wave- length 660 nanometers. According to  the  above  table, a sensor having such wavelength characteristics will be sup- 25 plied at the factory with a resistor 140 of one, and only one, resistance value, in this case shown to be  150  ohms.

The  sensor illustrated  in  FIG. 4 is designed  for use   inconnection with a processor 160 illustrated in FIG. 5 and designed to operate in conjunction with two LEDs M0, 120  30sequentially transmitting light to a single  sensor  130. However, the mechanism of the instant invention works equally well for processors requiring only a single LED and single or multiple photo sensors. The processor  contains  amicroprocessor   161,  and  a  read  only  memory  162  and  35random access memory 163. Table A (the same table used for calibrating sensor at the factory) no matter how extensive, may be easily programmed into ROM 162 at the time processor is fabricated. Current I from current   source169 is passed  through  resistor  140. The  resulting  voltage  40

(per Ohm’s law) is passed through multiplexor 166 through comparator 165, to microprocessor  161.Microprocessor 161 may be programmed to calculate the resistance  of  resistor  140  and  thereafter  to  look  up  the  45wavelengths of LEDs 110, 120 from Table A in ROM  162.

Microprocessor 161 is also programmed to itself recalibrate in current in detector 130 which passes through amplifica- tion and filtration circuitry 168 to multiplexor 166. Com- parator 165 and a digital to analog converter 170 are operative as an analog to digital converter means to present a digital signal to the microprocessor 161, thereby allowing microprocessor 161 to determine oxygen saturation and/or pulse rate. Results are shown on display   164.

In addition to the sensors 20, 22, 26, 28 and 30, the SCBA mask illustrated in FIG. 3 incorporates multiple position sensor systems 200 and 205 respectively. The position sensor system incorporates a distance measurement system in which a source of electromagnetic radiation 210 emits, for example, a laser beam and detects the reflected light from that beam. As an alternative embodiment the multiple sensor systems could be mounted on an air bottle harness, helmet, headband, or other piece of gear. The only requirement is that each set of sensors has its own known orientation with respect to any other set of  sensors.

FIG. 6 is a schematic illustration of the structure of the distance measurement system and its operation. For example, a laser source 215 is activated by the electronics system including a processor 220, clock 230, analog to digital (A/D) circuitry 240 and sensor amplifier 250. The beam of light travels through the air (medium) until it reaches an object (for example a wall). The light is reflected by the target object back towards the laser source (as well as any other line-of-site direction) with greatly reduced inten- sity. A light detector 260 (photodiode, photomultiplier tube, etc.), set to search for the same frequency of light as the source then begins to detect the reflected light. The time difference between the emission of light and its detection is carefully measured. The accuracy of the system will be proportional to the accuracy of the time measurement. The time measured represents the time taken by light to travel from the source to the target and from the target to the detector. This distance is twice the distance between the source and the target. Using the speed of light multiplied by the time measured and pided in half will provide the distance (Equation 1). For the example in FIG. 7, the time between transmission and detection is 10 nanoseconds (10x 10’ sec.). Thus the distance between the source and target is 5 nanoseco rids multiplie d b y the speed o f light (2.99792458x10’ meters/second) for an answer of 1.499 meters. Thus each nanosecond is approximately 0.29979 meters of distance.