A system and method are provided for using an oximeter to take blood pressure readings for an extended period of time. Calibration of the oximeter for this purpose requires use of a sphygmomanometer to determine a sequence of blood pressure readings taken for a patient over a sphygmomanometer duty cycle. During the duty cycle, readings for both blood pressure (sphygmomanometer) and blood flow amplitude (oximeter) are taken simultaneously at predetermined time intervals (e.g. patient pulse rate). These readings then determine an operational ratio between the two that can be used to translate pulse magnitude readings of the oximeter for presentation as blood pressure readings. Operationally, variations from the patient's systolic pressure can then be continuously monitored in real time.
