From the web:
https://www.healthline.com/health/normal-blood-oxygen-level#oxygen-levels
A pulse oximeter (pulse ox) is a noninvasive device that estimates the amount of oxygen in your blood. It does so by sending infrared light into capillaries in your finger, toe, or earlobe. Then it measures how much light is reflected off the gases.
A reading indicates what percentage of your blood is saturated, known as the SpO2 level. This test has a 2 percent error window. That means the reading may be as much as 2 percent higher or lower than your actual blood oxygen level.
This test may be slightly less accurate, but it’s very easy for doctors to perform. So doctors rely on it for fast readings.
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The article said people with nail polish or cold extremities (I have the later) will get a lower O2 number. 95 to 100 is a good number.
And for those who do NOT wish to spend beaux coos this little device is less than $5-10. Doesn’t cost a fortune.
Found at our local WalMart in the drug department; we asked the druggist for assistance.