When it appears, if you then switch to a low PO2 gas for five minutes as recommended, you should select that gas on your NHeO for the period you are breathing it, so that the NHeO can accurately calculate your decompression. If you do not tell the NHeO that you have switched to a low PO2 gas, it will assume that you have not switched. Do not forget to tell the NHeO when you switch back to your decompression gas.

ALTITUDE DIVING FAQ#1:
Do I have to do anything special with the computer when I am diving at altitude?
If you are diving at altitude, then you should switch the VR on at the surface before diving so that it can read the ambient atmospheric pressure.

Batteries
FAQ #1: Which batteries should I use?
Use AA batteries with 1.5 to 3.6V. Do not use AA batteries below 1.2V. Lithium batteries last much longer but have a very fast discharge curve.

FAQ #2 When should I change the battery?
Never remove the battery with the screen on. Always change the battery when there is still life in the unit. As a general guideline change the battery when the voltage gets down to 1.2V, (you will find the voltage reading on line 6 of your NHeO ’s start up screen.) Some lithium batteries need to be changed at even higher voltages.

FAQ #3 How do I change the battery?
Turn the NHeO on then let it turn itself off. (If it will not turn on see FAQ#4). Insert the battery positive end first into the compartment. (If you insert the battery negative end first, it will not damage the NHeO but it will not function.) Screw down the battery cap until no O ring is visible and the thread bottoms out. (Always keep the thread clean as the thread is the earth for the battery.)

FAQ #4 Too late; my battery went flat! What do I do now?
Remove the battery. Wait at least 10 minutes. Insert a new battery and screw the battery cap in slowly until you see the screen flash once. Stop and let the NHeO turn itself on (,you will see the time change screen,) then allow the NHeO to turn itself off again. NOW FINISH SCREWING THE CAP TIGHTLY. You will now be able to switch the NHeO on normally. If the NHeO appears to freeze with data showing on the screen, leave it for 2 minutes and it will reset itself. If the NHeO appears to hang, repeat the procedure outlined in this FAQ.

FAQ #5 How should I care for my battery cap O-Rings?
Treat them like O rings on an underwater camera housing. Keep them lightly greased, change them if they become damaged or worn and as a basic rule of thumb, change them after 10 battery changes even if they do not look damaged or worn.

FAQ#7 My NHeO resets underwater and loses gases and defaults to air
When using some 3.6v lithium batteries they are too tight in the battery cap, the negitive end of the battery needs the outer plastic skin removed. This allows a better contact with the battery. Also check the battery cap is fully screwed in.

FAQ#6 When I changed my battery I lost all my logged dives?
Before changing the battery allow the NHeO to power down (switch off). Then change the battery as FAQ#3

Dead NHeO
FAQ #1 My unit froze at depth or turned off while diving. What can I do?
It is likely that you have allowed the battery to run out before replacing it. Go to Battery FAQ#4. Following this procedure will usually solve the problem. If the unit appears to freeze at a depth this could also be due to a low battery. Please read FAQ#4 on battery changing. It is appears to switch off and sometimes switch on again while diving, there may be corrosion in the battery cap due to a leaking battery. If a faulty battery has leaked, clean in side the battery cap and the battery compartment. Wire wool or Emery paper may be required. Remove the battery cap spring and clean around it. Spare battery caps are available through VR Technology. If this is does not solve the problem, send your NHeO back to us using the GRN form together with a recent history.

FAQ#2 My NHeO switches off at depth and switches on again when shallow
When using some 3.6v lithium batteries they are too tight in the battery cap, the negitive end of the battery needs the outer plastic skin removed. This allows a better contact with the battery. Also check the battery cap is fully screwed in.

High PPO2 warnings
FAQ#1 Iam diving on a gas and have no "deeper" gas to switch to the high PPO2 warning does not appear unit I reach a PPO2 of 1.8?
This is not a flaw or bug in the computer. This is how the computer works and has always worked.
The high PPO2 warning is just that,it warns as soon as a diver's PPO2 reaches a dangerous level and there is no deeper gas in the gas list to switch to. It is not an "MOD exceeded" warning, the NHeO has no such thing. The diver presets an MOD for each gas and it is the diver's responsibility to remain above this MOD.An indication that a diver has exceeded an MOD of 1.6 would be a rapidly climbing CNS% reading and shortly after that, depending on what level the diver has set as his warning %, an air break warning would appear.
The philosophy behind the design of VR computers is that they tell a diver what he is doing and imform him of the conseqences of his action; their task is not to teach or punish.

Light Modes
FAQ #1 What do the abbreviations for the five different backlight modes in the DVo screen mean?
Tm …………Light on for 10 seconds at the surface or underwater
DTm…………Light on for 10 seconds underwater
On…………...Light always on at the surface and underwater
DOn…………Light off at the surface, light on underwater

PC Link (This is a factory fitted option only)
FAQ #1 My PC Link does not appear to work.
The PC Link option must be purchased with the NHeO. Alternatively, the PC Link can be fitted later as an option but the NHeO must be returned to the factory for the fitting.

Switches
FAQ #1 The switches are not operating smoothly. What can I do?
The switch pockets are sealed and separate from the main unit. Occasionally sand or dirt may become lodged in the pocket and impede their operation. To remove this slightly depress the switch and clean the pocket out with a jet of fresh water. A SMALL amount of light engineering oil, (NOT grease) may help improve switch action in extreme cases.
FAQ #2 One or both of the switches does not seem to be working. Is there anything I can do?
If the apparent switch malfunction has taken place after a battery change and your NHeO will not power up at all, see FAQ #4 in the Battery section for a possible solution. In other circumstances, if the switch seems to be moving correctly but the NHeO still does not respond return your NHeO to us at Delta P for maintenance and repair, including a note on the problem and recent history of use. The switches are not user-repairable.
FAQ#3 NHeO won’t change screens
This is an indication that one of the switch buttons has cracked and needs replacement. To check, pop both the out switches, (instructions on Maintenance page in manual), and check them. If one or both are broken, contact your dealer for a replacement set, (you might also like to buy a set to keep in your spares kit, especially if planning a long trip.)

Use Tables
FAQ #1 “USE TABLES”. On a recent dive “USE TABLES” appeared on the screen while I was ascending. What does that mean?
If you ascend past a required micro-bubble deep stop or a decompression stop ceiling you will see a DESCEND message and a sixty second timer starts counting down. If you return to below the ceiling before sixty seconds have elapsed then the timer will start to count back up to 60 again and when it reaches 60, the NHeO will resume its calculation of your decompression profile. Depending on the extent of your excursion you should build in safety factors for the remainder of your decompression. If you ignore or do not notice the DESCEND warning, after 60 seconds the “USE TABLES” message will appear. After this, the NHeO will continue to display decompression data but this will be “Best Guess” and cannot be relied upon. You should switch to manual back-up tables for the remainder of the dive.