In 1896, Scipione Riva-Rocci invented an easy-to-use version of the mercury sphygmomanometer to measure brachial blood pressure. Determining the systolic and diastolic blood pressures by listening to the Korotkoff sounds through a stethoscope inserted under the pressure cuff is called the auscultatory method. The pressurized cuff around the arm blocks the passage of blood through the main artery, either partially or completely, depending on the pressure. The oscillometric method eliminates the need for a stethoscope and lends itself better to electronic measurement devices. Although somewhat less accurate, the oscillometric method is commonly used in automatic electronic blood pressure devices commercially available today. The pressure sensor is made in the form of a Wheatstone bridge using four strain-gauges with a differential output. The resistor network in the offset trim circuit is designed to produce a small positive or negative voltage around the ground potential by adjustment of a trimpot.