A totally hands-on demonstration of how blood pressure is measured! Presented to my kid's second grade class years ago. I promise I will write up full instructions for this but it's too cool to not upload now. Okay, here's the idea - replicate a mercury sphygmomanometer using a glass peanut butter jar with colored water and a clear plastic tube. Buy a blood pressure cuff and stethoscope from your favorite online auction house. Cut the tube to the stethoscope and attach a microphone and play through an amplifier. Cut the tube to the pressure gauge and connect it to the peanut butter jar. Pump the cuff until you can't hear your pulse anymore, then open the valve to slowly let out the air. Note the height of the water when you can just start to hear the heartbeat, and when it disappears again. These are your systolic and diastolic pressures, but because we're using water, divide the number of millimeters of water by 13.6 to convert to millimeters of mercury. And you're done!!!