Pulse Oximeters
I enjoyed the article on pulse oximeters (March 2013). You can also buy them at Walgreens or Walmart for $30 to $40. I have an Oxywatch C20, which I bought a few years ago at Walgreens for around $40. It is within one percent of what is used at my medical clinic.
You mentioned that the units tested were within “two percentage points” of the medical unit. This can be misleading as one can control the level on the pulse oximeter by altering one’s breathing. Most people breathe shallowly. So with the pulse oximeter on a finger reading say 94 percent, one can take very deep breaths and in a minute or two temporarily raise the blood-oxygen levels up to four or five percent.