12 sets of infrared sensor heads before and after, to avoid leak detection Four-sided hollow design to prevent airflow interference Simultaneously record 40 sets of speed and energy data for easy viewing Working voltage: DC3.7-4.2VAlready builtlithium battery) Working environment temperature: -30C- +60C Accuracy: test error1% Measuring range: 1-800 M/S Other: the four sides of the hollow design, not only visual field, but also to alleviate the impact of airflow measurement. Improved stability and accuracy of the test.To measure the velocity of the projectile propelled by the air pressure, please measure the distance from the machine 4-8 cm, so that the air flow can be to get stable and accurate data Function: velocity measurement /Speed energy/ Look through records Color: Black Material: Metal+Plastic Package Contents: 1set x speed meter Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.