In a method and apparatus for measuring extreme blood pressure values during a single non-invasive blood measurement, the time intervals between sequential heartbeats are measured for a series of heartbeats in an oscillometric blood pressure measurement time period. Oscillometric blood pressure measurement data for the heartbeats of the series is obtained and associated with the heartbeat time intervals. An average time interval between heartbeats is also determined. A first data bin may be defined for blood pressure data associated with time intervals that are longer as compared to the average time interval. A second data bin is defined for blood pressure data with time intervals that are shorter as compared to the average time interval. The measured oscillometric blood pressure data is sorted into the data bins in accordance with the associated time intervals. The data in the first data bin is used to derive a high systolic blood pressure value and a low diastolic blood pressure value. The data in the second bin is used to derive a low systolic blood pressure value and a high diastolic blood pressure value. A typical blood pressure value may also be determined.