Taking blood pressure measurements correctly is essential in order to successfully evaluate a patient's blood pressure from the initial measurement and subsequent measurements over time. With the purpose to determine if the time between blood pressure measurements in an office or clinic bears an influence on any variation in measurement, a study was carried out under which two blood pressure measurements five minutes apart were taken using an automatic instrument in order to evaluate the existence of any differences as well as to identify which arm should be the control arm and to evaluate the absolute measurements between both arms. During this study, the authors observed a decrease in the mean for the repeated blood pressure measurement of 7.7 mmHg (IC 95%: 4.7-10.7 mmHg, p < 0.0001) for the systolic measurement and of 2.9 mmHg (IC 95%: 1.6-4.2 mmHg) for the diastolic measurement. 78% of the patients in this study registered a difference between the two measurements, either systolic or diastolic > or = 5 mmHg. It was not possible to establish a significant relationship between the decrease in these blood pressure measurements and factors such as age, sex, cardiac frequency or hypertension. The control arm was the right arm in 59.3% of the patients. The absolute mean of the differences between both arms was 8.4 mmHg (IC 95%: 6.8-10 mmHg) for the systolic measurements and 5 mmHg (IC 95%: 3.9-6.1 mmHg) for the diastolic measurements. 26 patients, 44.1%, registered a difference in pressure between their arms > or = 10 mmHg.