Oscillometric blood pressure (BP) measurement devices are increasingly replacing standard mercury sphygmomanometers and generalizability of validation studies to other environments, for example, national survey environments, is assumed. We compared BP measurements according to two highly standardized German national survey BP protocols: a standard mercury sphygmomanometer and an oscillometric device, Datascope Accutorr Plus, each with specific manufacturer-provided cuffs and cuff-selection rules. A sample of 105 adults were subjected to alternate same-arm BP measurements according to the principles of the International Protocol revision 2010 for the validation of BP-measuring devices in adults of the European Society of Hypertension. In all, 315 BP measurement pairs were obtained. The mean systolic blood pressure (SBP) and diastolic blood pressure (DBP) were higher by the standard mercury old protocol and increased with BP, age, and pulse pressure, and were associated with the ratios of the cuff width to the arm circumference. The mean systolic difference (datascope new protocol-standard mercury old protocol) in participants with old protocol: for SBP<120 was -3.5 ± 4.9 mmHg (n=162), for SBP 120-139 (n=108) was -6.4 ± 5.8 mmHg, and for SBP ≥ 140 (n=45) was -11.9 ± 7.2 mmHg. For DBP<80/80-89/≥ 90 in 230/67/18 participants, the differences were -1.9 ± 5.0/-6.8 ± 5.9/-7.6 ± 5.2 mmHg. A calibration formula for SBP derived from linear regression modeling includes SBP, sex, age, pulse pressure, and the difference in the cuff-width to arm-circumference ratios for the two devices (for DBP without age). Our study suggests that even in a highly standardized national survey environment, reported agreement from validation studies may not be replicable and comparisons in the specific clinical or research setting can be useful before replacing the mercury device completely.