Before using your gas test gauge, you should zero your tool to ensure that the readings it provides are accurate. The fluid levels on both sides of the u-tube should be at 0 mbar before you take your measurement.
Readings on a gas test gauge should always be taken from the lowest point of the meniscus (the curved surface of the liquid).
To zero your gauge, move the scale using the zero adjuster until the fluid levels are aligned with the 0 mark.
You are now ready to begin using your gas test gauge.
