Even if you're recertified 3, 4 or 5 times, the nerves and the sweat glands still get a major workout during hands-on testing.  If you prepare ahead of time, relax, don't be in a hurry and don't use "short cuts", you will probably do just fine.

We are all familiar with the Double Check valve test procedures and the requirement to hold the gauge at the proper height.  The procedures, at this time, do not specify the exact moment when the gauge must be placed at the proper height.  However, there is a critical moment during the test when the gauge must be placed at the proper height.  That critical moment is before the #1 shutoff valve is closed.  It can be done any time before closing the #1 shutoff valve, but if the gauge is not at the proper height when the #1 shutoff valve is closed, the proctor must consider that an error.

The logic behind this is fairly simple.  If you close the #2 shutoff valve and that valve is leaking, the gauge will remain virtually unchanged because the inlet valve #1 is still open, supplying constant pressure.  As soon as you close the #1 shutoff (#2 shutoff valve is still leaking), the differential reading on the gauge will begin to drop.  If you position the gauge at the proper height before closing the #1 shutoff valve, you will get an accurate differential reading for the check valve.  If the gauge is not at the proper height when the #1 shutoff valve was closed, the differential reading on the gauge will be inaccurate.

By the way, the critical moment for positioning the gauge at the proper height while testing the PVB is exactly the same, i.e. before you close the #1 shutoff valve.  One thing to keep in mind is that proctors are required to view your actions and determine whether your actions could have caused erroneous results.  Whether or not your action actually did cause erroneous results is not the issue.

The proctors I know and have worked with are all hoping you do well.  We know how upsetting it can be when you make a mistake, especially when it's due to nerves or being in a hurry.  So stay away from the double cappucinos and remember, no one ever died from failing a Hands-On Test...Yet.