“…Additionally, Chowdhury developed an amplitude modulated ultrasonic method with an infrared technique [ 6 , 17 ]. The method of measuring Hb by spectrophotometry has included use of several wavelengths, such as 532 nm [ 18 ], 542 or 574 nm with 900 nm [ 19 , 20 ], 545 nm [ 20 ], 660 nm [ 21 , 22 ], 600–750 nm [ 23 , 24 ], 700 nm [ 25 , 26 ], 760 nm [ 20 , 26 ], 850–1000 nm [ 23 , 24 ], and 940 nm [ 22 , 27 ]. This method has a high degree of accuracy, is painless (there is no need to injure the patient), has lower variable costs, can be used repeatedly, and has no consumable costs.…”