It starts off by passing beams of light through your blood to measure the amount of oxygen in it. This is a noninvasive way of testing your levels.
You won't be able to feel the small beams of light being passed through your blood. Think of it as a scanner. If you've ever used a copy machine before, then you know it's noninvasive. It simply takes images of whatever you place on the sensor.
Now that you know what a thumb paino is and what the different types of them are now you have to learn how to play one. Like with any instrument the first step is to learn how to hold it properly. Learning this will help the notes be played properly and will help you have more ease when playing. You properly hold by using the sides of the palms of the hands and then comfortably placing your thumbs onto the tines.