NCT's should not be used in Override, nor should the High Intensity headrest switch be locked on.
Override should only be used when the patient is very difficult to fixate and align in the reticule.
In a nutshell, override eliminates the verification signal which, when the instrument is in the "Red Dot" or "On" position, only allows the machine to be fired when the patient is properly lined up, thus insuring an accurate reading.
This works in conjunction with the High Intensity Switch. When the switch is not locked on, the operator will know the patient is properly aligned because the light will dim if they back their head away. By locking the unit in high intensity, the user will not know if the patient moves away when taking the reading. When the override is engaged, this can result in an inaccurate high reading.
Many technicians use the unit in override, with the high intensity switch locked because it is easier & quicker to take a reading. We discourage this for the reasons listed above.
The operator must be sure to clean the glass ring surrounding the air tube regularly. When this is not done, reflections off the eye, along with dirt and dust form a film on the objective. When this film becomes too dense, the verification signal is cut down and the machine never knows it is focused. The incorrect thig to do is to switch to "Override" and eliminate this signal.
The first thing to do when a user says the unit will only work in "Override" is to make sure they clean the objective. We eliminate over 1/2 of our potential NCT service calls with this easy step. It is also critical to make sure the target lamp is replaced. These lamps have a tendency to darken & form a silver film very gradually, so in many cases the user does not realize how dim it is becoming. This also makes it more difficult to take a reading since the red dot is faint. We would be happy to supply you with an NCT PM Kit, which includes complete instructions, bulbs, forehead pads, Q Tips and the Allen Wrenches needed to open the unit & replace the bulb, Just contact us & order part 12415.LAMP