Cold fingers can affect the accuracy of blood pressure readings with OptiBP, due to a process called vasoconstriction.
Vascoconstriction occures when blood vessels are constricted, resulting in a reduction of blood flow to the affect area. Thus, making it difficult for OptiBP to get a reading of your fingertip blood flow.
Warm up your hands: Hold your hands under warm water or rub them together to increase blood flow to your fingertips.