At the doctor the nurse usually puts on your finger an Oximeter to measure pulse & oxygen level. What is the..

... normal oxygen level? The mid-to-high 90's? If your score is in the low 90's, is it bad and what might that indicate health-wise?

Pulse oximetry measures the percentage of hemoglobin (Hb) saturated with oxygen. This oxygen saturation is a measure of how much oxygen the blood is carrying as a percentage of the maximum it could carry.

Pulse oximetry is performed simply by placing a special light clip on your finger, earlobe or toe. The clip is attached to the pulse oximeter by a cable, which is connected to the pulse oximeter computerized unit. The pulse oximeter monitors the oxygen saturation in the blood.
The testing is non-invasive and does not cause pain, nor is it considered a "risky" procedure. Pulse oximetry can be performed at rest, during activity or even during sleep.

A pulse oximeter passes two light waves (red and infrared) through the skin to measure the amount of oxygen in your blood.

The oximeter detects the slight change in color of the arterial blood caused by the beat of the heart when blood is pushed into the finger (or earlobe or toe). Because the change in color is so minute, it is imperative to ensure a strong pulse during testing. When the pulse is weak, the results may be inaccurate.

Pulse oximeter results must be accompanied by the percentage of oxygen the person is breathing, and their respiratory rate, for the results to be meaningful.
A fit, healthy person should have an oxygen saturation between 95% and 99%. Results lower than 90% may be caused by excessive bleeding, lung problems, cigarette smoking, blood vessel problems, lung diseases such as COPD. Percentages above 99% may indicate that the testing was performed outside the pulse oximeter's limitations; re-testing may be needed.

What the Results Mean
One Hb molecule has the ability to carry up to four oxygen molecules. Therefore, one hundred hemoglobin molecules could carry a maximum of 400 oxygen molecules. If during testing, the hemoglobin molecules were carrying 380 oxygen molecules, the percentage of saturation would be 95% ((380/400) x 100 = 95%).

Well of course 100 is perfect and thats rare that someone is at 100 on their own but if you get into the 80's and low 90's then you need a little help breathing