this really is a physics question! (I think) so, when you measure blood pressure, you wrap a cuff around the subject's arm and fill it with air past the point where the artery is occluded. Then, you listen with a stethoscope as you slowly release the air...you'll be able to hear beats for a range of pressures. These beats signify that the blood flow is obstructed and the top and bottom numbers read give the systolic and diastolic blood pressures (pressure during compression and relaxation of ventricles, respectively). Make sense? Ok, so the cuffs come in different sizes and are calibrated accordingly. If you use the wrong size cuff on a person's arm, you get an inaccurate reading. For a cuff that's too large for the arm, the bp comes out lower than the true pressure. And here's where my conundrum is, bc that doesn't make sense! To me, it makes sense that the cuff, being too large, might possibly give an abnormally high reading because it's harder to make snug on the arm and therefore would require more pressure to occlude the artery...but I can't think of any reason why the cuff would give a low reading. does anyone understand the physics behind this?