Below is a link to the Omega video manuals, and you can select the Seamaster 300m. The manuals for other dive watches are probably similar.

The video states that a diver puts the illuminated dot at the minute when starting the dive to see how long he has been diving. I've always understood that the illuminated dot should be at the surfacing time. So if you are going to start surfacing at 20 minutes, you put the bezel's 40 maker where the watch's minute hand is when starting the dive. That way the minute hand counts down toward the dot and clearly shows when it's time to surface. It can be really hard to tell if the minute hand is 17 minutes or 22 minutes from the dot, but it's very easy to see when it's at the dot or past the dot.

https://www.omegawatches.com/en-us/customer-service/user-manuals

 

I don't dive but I always understood that the dot is put at the minute hand upon entering the water and it counts elapsed time.

 

Pretty sure you allowed to use the bezel in the way that best works for you. Don't sweat it.

 

I agree you can use any way you want. When I swim, I use it as a set counter. But counting up the way on the site seems dangerous. It's harder to know when to surface. You could have an issue and not clearly remember the surfacing time.

 

I think most divers actually use a dive computer, and use the watch as purely a back-up so not sure I would call Omega's advice dangerous...

But if you feel so strongly about it, email Omega and tell them they should change it.

 

As instructions go and diving without a computer.

The timer is set upon going under water, you set the timer is set by moving the bezel pip at zero to the minute hands.

Now with the advent of diver computers. You could use it to time your surface interval if your not wearing a wrist mount computer and want to keep track while walking on the boat. In theory this way upon surface you reset it again as the back up was not needed and you do not need to track submerged time.

If your diving with it as a backup to a computer as intended you set it upon submerging.

I’m a certified rescue diver, the highest non professional certification you can earn.

 

@bz0123

I just red read your post. I thought you where talking about timing the surface interval in the wake of dive computers.

While diving planned down time is not tracked. Total downtime and max depth are tracked to apply to the dive tables. Computers allow for diving at multiple levels which is not covered by basic tables. While old school and taught basic dive tables assume a dive is all at the max depth achieved.

Setting a countdown as you imply would be dangerous as sometimes dives do no go as planned. And in the event of something unplanned doing a conversion of planned downtime to extended downtime would be a bad idea and could cause confusion if an emergency occurred. Ie you planned a 25 minute dive to 80feet and someone got stuck in a fishing line. Your now over the time and you would not be 100% sure of max downtime. It’s better to use the count up and use that display to track downtime.

Does that make sense?

 

Thanks for the reply. It seems like if you planned a 20 minute dive and had to extend for some reason, that you could easily add the extra time when you surface. Essentially you have the same running clock, you just have to know the original dive time. Setting the dot at the minute hand, you see 24 minutes past the dot. Setting the dot for you are supposed to be surfaced, you see that you are 4 past the dot for 24 total.

I'm not an experienced diver, but if the dive watch was the only timing device, I would think the diver would want the surface time to clearly visible if all he could see was the lume.

All this is probably moot with dive computers.

 

No since your planning on a failure. It’s easier to remember your plan when things are peachy. It’s more important to quickly know your total downtime not remember your plan if something goes sideways.

Additionally many dives are planned without a set downtime.

Example. Wall dive with mild current running perpendicular to the wall. Plan is submerge to 60 feet then swim into the current along the wall till tank at 60% pressure on the lowest diver. Rise to 40 feet then swim back the other direction and surface on the anchor or just before the boat. You go a tad longer as the 2nd half of the dive is lower depth and lower air consumption.

For a straight forward dive at a fixed depth i rather plan around the current swim into it till you hit 70% then reverse course. For a wreck dive (non penetrating) you and your buddy agree on a safe tank level before setting on a return to surface with safe reserves.

Out of my hundreds of dives I can count on one hand the non teaching dives I’ve done with a fixed downtime while using a computer. The computer allows you to work around no deco dives, and if you break into deco you plan around it. I always safety stop at 20-15feet for a deco stop anyways.

 

Thank you for the very detailed answer.