Thanks, David, for your comment on that. The higher pressure at the wrist is due to pulse pressure amplification along the arterial path, not the vessel diameter. The problem with measuring BP at the wrist is about positioning the wrist-cum-device at the level of the atrium. That's difficult, and best achieved with positioning the cuff at the brachial artery. That's why measuring BP in supine position might deliver higher results than in seated position (in supine position, the upper arm may be below atrium level). But as you correctly mention, the reference values are typicall from seated position and brachial cuff occlusion.