The Pen-Style Liter Meter measures Oxygen flows from 0-10 liters per minute. Small and lightweight liter meters quickly verify the flow of gas. Simply attach your supply line to the bottom of the meter while holding it in an upright vertical position. Small, lightweight device used to verify the flow of oxygen Reads 0-10 liters/minute by attaching to the oxygen supply line, holding upright in the vertical position and locating the center of the ball Works with tanks and concentrators This product is only to be used for quick assessment of the flow of gas, it is not to be used as a calibration device