Each finger and hand are likely to show different results. It is because the level of perfusion varies from finger to finger. Some fingers might be in motion while others are inactive, and this causes variations in the results. Factors like skin pigmentation, wearing nail paint, and vasoconstriction also lead to different results on different fingers. Smoking can also lead to inaccurate results. Therefore, the best fingers to take the reading are the right hand's middle finger and thumb. Studies have revealed them to be the most accurate determinant of the SpO2 level when all other factors are accounted for.