A physician's office or other medical provider should really not be using a $20 aka OTC pulse oximeter. Those are not cleared (i.e. tested) for medical purposes and have widely varying accuracy
The FDA is informing patients and health care providers that pulse oximeters have limitations and a risk of inaccuracy that must be considered.
www.fda.gov
- Over-the-counter (OTC) oximeters are sold directly to consumers in stores or online and include smart phone apps developed for the purpose of estimating oxygen saturation. Use of OTC oximeters has increased as a result of the COVID-19 pandemic. OTC oximeters that are sold as either general wellness or sporting/aviation products are not intended for medical purposes, so they do not undergo FDA review. OTC oximeters intended for medical purposes undergo review by the FDA and require premarket authorization.
Then some are okay and some or not:
Many low-cost pulse oximeters sold to consumers demonstrate highly inaccurate readings. Unexpectedly, the accuracy of some low-cost pulse oximeters tested here performed similarly to more expensive, ISO-cleared units when measuring hypoxia in healthy subjects. None of those tested here met World...
pubmed.ncbi.nlm.nih.gov
You have to research the exact brand and model (accuracy varies within brands...)
Another issue is that low-quality models don't adapt well to different patients' pigmentation nor movement.
A medical grade model costs like $600 (or builtin to an otherwise more powerful multifunction device) which should be within reach for just about any medical office...