Instant Selection from up to Nine English/Metric Units. Stores 20 Readings in Memory for Later Reference. Measures Positive, Negative or Differential Pressures. Large Easy-to-Read 0.4" LCD Display Includes Switchable Backlight for Great Visibility-Anywhere! Both Audible and Visual Overpressure Alarms. Includes + and - Indicators plus Low Battery Warning. Operates up to 100 Hours on one 9 Volt Battery. Series 477 Handheld Digital Manometers are packed with features you need to make low pressure measurement and recording faster, easier and more accurate than ever. Now you can instantly select from up to nine popular pressure units without having to waste time with tedious conversions. Plus, a versatile non-volatile memory function enables storage of up to 20 readings - perfect for HVAC technicians making Pilot tube traverses of airflow through ducts. A display HOLD key temporarily freezes the current value for situations where pressure fluctuates. To protect against overpressure, both usual and audible alarms are included. Audible alarm also sounds to indicate a value has been stored in memory. PHYSICAL DATA Accuracy: ±0.5% of full scale from 60 to 78°F (15 to 25°C); ±1% of full scale from 32 to 60, 78 to 104°F (0 to 15, 25 to 40°C). Storage Temperature: -4 to 176°F (-20 to 80°C) Pressure Hysteresis: ±0.1% of full scale Maximum Pressure: See chart below Pressure Connections: Barbed, for 1/8" or 3/16" I.D. tubing Power Source: 9V alkaline battery, included Battery Life: Up to 100 hours of operation. Less when LCD backlight is used. Pressure Display: 0.4" liquid crystal Size: 6 9/16"H x 2 13/16"W x 29/32"D (166x71x23 mm) Weight, Battery Included: >12 ounces (340 grams)