This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
This law of plethysmography explains principle of working in 
Select and explain. 
A. Capnography, B. Oximetry, C. CVP monitor, D. Entropy
B: Oximetry
Answer: B: Oximetry 
Explanation: The  law of plethysmography explains working of pulse oximeter.