Multi-wavelength oximeter having a means for disregarding a poor signal

An oximeter for measuring oxygen saturation in arterial blood comprising:

• light source means for projecting light to a body member to be measured;
• light responsive means for receiving the light which has transmitted through said body member and for generating at least first, second and third signals at three different wavelengths;
• detecting means for detecting whether or not an amplitude level of each of said first, second and third signals is within a predetermined range between upper and lower levels;
• selecting means for selecting first, second and third signals which have been detected by said detecting means;
• calculating means for calculating at least first oxygen saturation data using selected first and second signals and second oxygen saturation data using selected first and third signals;
• determining means for determining whether or not a difference between said first and second oxygen saturation data is within a predetermined level;
• and
• means for designating said first and/or second oxygen saturation data as valid when said difference is within said predetermined level, and as invalid when said difference is not within said predetermined level.