Classic Hand Aneroid from Welch Allyn, the company with nearly one hundred years of experience designing and building the most accurate and durable aneroid sphygmomanometers in the world. Certified accurate to ±3mmHg. Trigger deflation valve provides smooth one-finger control. Latex-free for safety. Thermally treated diaphragm maintains calibration. Ergonomic design works well in right or left hand.