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Your SAC Rate and Average Depth - in part and in total

Sometimes we have a dive where we get obsessed with analyzing it afterwards. Or maybe you're like that all the time! Either way, wouldn't it be nice to look at a "piece" of the dive?


On the Environment tab, if all of the required information about your tank is filled in, you can get a SAC Rate (RMV) over the length of the dive as shown in the photo above. If you only used one tank over the course of your dive, then the SAC rate for this tank will also be for the whole dive. Unless you're doing some technical multi tank diving, this is the case for most people.

Dive Log, Dive Log Manager, and DiveLogDT all use the Respiratory Minute Volume (RMV) method of calculating your SAC rate so that you can compare your rate over *all* your dives, regardless of which tank (size) you used. This is the volume of gas you breathed in 1 minute at the surface. If you use Imperial units, it will be "cubic feet per minute", and if you use metric units, it will be in "liters per minute". You can use this number to plan a future dive, regardless of what kind or size of tank you will use.

If you want to take a "deep dive" into analyzing your SAC rate for a particular dive, you can do this on the profile tab. (This assumes you have a dive computer that logs your tank pressure over the course of your dive).


In the image above, we're looking at the same dive as the first image, however we're looking at just a portion of it. By "clicking (and holding) and dragging" over the time axis of the graph, you can select a *portion* of time and find out what your average depth was for that portion, and what your average RMV rate was for just that portion.

From the images, we can see that Jane Diver had an average RMV rate over the course of the whole dive of 0.34 ft3/min and an Average Depth of 47 ft. But in the second image, while starting her ascent at the end of the dive, she had an average RMV rate of 0.26 ft3/min while still maintaining the same Average Depth. Apparently she was much more mellow on her way back!

When clicking and dragging, you can look at the "Time" value at the top of the profile to determine exactly what portion you are looking at. It will change when you click, and update when you drag, so that if you want to know exactly the period of time you're analyzing, you can.

We have had some requests from customers to show a different kind of SAC rate calculation, sometimes called "Surface Gas Consumption". This is an absolute measure of gas over time, and is only useful when using the same kind and size of cylinder over subsequent dives. It is simply the amount of gas you have used in a period of time, adjusted to the surface pressure. Again, if you're using Imperial measurements, this number will be in "psi per minute", and if you're using Metric units, it will be in "bar per minute". We have added an Application Preference to toggle between the two kinds of SAC measurements. If you open the Preferences Window, navigate to the Profile tab, you will see a checkbox at the bottom "Calculate SAC (not RMV)". If this is checked, you will instead see a "SAC" rate when selecting a portion of the dive as above. The image below will show SAC rate using Metric units.


Happy Analyzing! Happy Diving!

Quick Add - Logging in a hurry

If you have used our software, you know that it logs individual Dives, and that a Dive can have many other items associated with it, such as a Dive Site or Equipment or a "tag" called a Dive Type. When logging a dive, sometimes you have lot's of time afterwards to sit and record everything in great detail and luxuriate over the details while you remember what a great time you had. But let's face it, sometimes you need to just quickly "get it done" so you can do something else. That's when you may want to do a "Quick Add" of an item while you're logging your dive.

You can "Quick Add" any of the dropdowns on the Detail tab of a dive. Just type in the name and tab to the next thing. If that name doesn't already exist in the list of those items, you'll get a small bubble window telling you that the new item has just been added. This works for Site, City, Country, Shop, and Trip.


When there is a list of items that can be added, you can also add a new one by clicking on the "plus" sign in the upper corner. Once clicked, you'll get a popup window you can just start typing in. Hit return and the new list item has been added and you can continue logging. This works for Buddies, Dive Types, and Equipment.


Happy Diving! (and Dive Logging!)

Dive Log, DCbuddy and the Suunto Vyper Novo and Zoop Novo

The current shipping version of Dive Log for iOS contains support for downloading Suunto’s latest dive computers using DCbuddy. You can download the Vyper Novo and the Zoop Novo by choosing the Manufacturer “Suunto” and the Model “DX” on the DCbuddy download screen. Dive Log will automatically detect that you are talking to a Vyper Novo or Zoop Novo and will parse the downloaded data appropriately. The next update to Dive Log will add the Vyper Novo and the Zoop Novo to the list of Models on the DCbuddy downloads page.

The Vyper Novo and the Zoop Novo use the “DCbuddy - Suunto D” connectors rather than the “DCbuddy - Suunto Z” connectors used by previous Vyper and Zoop models. If you already have a DCbuddy and just require just the pigtail connector those are available from the DiveNav Inc. website (

Dive Log also recently added support for the Oceanic DataMask and the Aeris CompuMask. These computers use the "DCbuddy - Pelagic V” connectors.

UWatec :: Does anybody really know what time it is?

UWatec :: Does anybody really know what time it is? Does anybody really care? If you’re logging dives, you bet! (If you’re too young to get the song reference, you might want to look it up for clarity)

If you’re downloading your “later generation” UWatec dive computer, and you’re getting the wrong start time for your dive, you're going to want to read and understand these details. If you’re just interested in more detailed information about using your dive computer, this might be interesting.

Your UWatec dive computer keeps track of time using “Coordinated Universal Time” or UTC. It is the primary standard by which the world regulates clocks and time. It is similar to, but not exactly the same as, “Greenwich Mean Time” (GMT). GMT is a time zone whereas UTC is a time standard. No country uses UTC as a local time, but some use GMT as their local time zone. The “UTC time” is the same everywhere in the world. It is the same everywhere in the world at the same time.

Screen Shot 2015-12-23 at 9.42.43 AMOnce you have agreed what UTC is, then the local time where you are is measured as an “offset” from UTC. The offset can be either a positive number, or a negative number. On the day of this blog post, Belgium has a UTC Offset of +1:00. The Pacific coast of the USA has a UTC offset of -8:00. This is very similar to saying that your time zone is +1 from GMT or -8 from GMT, it just formalizes and standardizes the language. Your Mac also uses this concept to determine what time it is. When you travel with your Mac to a new place, you don’t go in and change the time, you just change the time *zone* to match and then your Mac knows what the local time is.

When you are setting the time on your UWatec, your instructions show you how to set both the time of day and the UTC offset. The idea is that when you travel to another time zone to dive, you simply change the UTC offset to match where you are now diving. This UTC offset is saved along with all the other information specific to a given dive so that it knows what time it was when you did the dive, even if you change time zones again after the dive. (Otherwise the start time of an “old” dive would change when you changed the current time zone or UTC offset setting).

Now that you have all that terminology, follow along here and see how the “time of day” on your dive computer can look right, but actually be wrong.

I’ll use the Pacific coast of the USA as an example because it has a large difference from UTC. Let’s say you don’t bother setting the UTC offset on the dive computer (so it’s set to 0), and you just set the time of day to be “right”. What you’ve just done is (re)set the dive computers version of the UTC value to be 8 hours wrong. Even though the dive computers time of day always matches what is shown on the wall clocks around you, when you download it, the logbook software will read a dive and see, “oh look, the UTC offset for that dive was zero”. I’ll just “add zero” to the current UTC value given to me by the *Mac* and that will give me the start time of the dive. Using actual numbers, let’s say your dive computer says 09:00 when you start a dive. In UTC time, that’s actually 17:00. When downloaded, the start time of that dive will be calculated as “+0” from UTC or 17:00. Not really what you wanted. When you look up the start time of the dive on the UWatec though, it will show what you really want to see, which is 9:00. Looks right, technically wrong.

What the UWatec instructions don’t really tell you is that you should find out what your UTC offset is where you are, and set that FIRST. And then go in and adjust the time of day if you need to. In the example above, the diver should first set the UTC offset to -8:00 and then set the time of day to be correct, if necessary. This will set the correct UTC value for the UWatec. Then when the software downloads the dive information, it says “oh look, the UTC Offset of this dive is -8, therefore the start time is 17:00 minus 8 hours or 09:00”.

Screen Shot 2015-12-23 at 9.42.56 AMWhen you buy a brand new “out of the box” UWatec Galileo, it seems likely that the UTC value is already set and already set correctly. Having never bought a new one myself, I can’t say for sure.

When traveling, you can also look up and set the UTC offset before you leave. If you’re heading off to Bonaire on a dive trip, they are “UTC -4:00” right now. So set the UTC offset to -4:00 before you leave and you’ll know that your dive computer will have the right time of day for when you arrive and start diving. (And yes, we’ve all jumped in the water on our first dive of the trip and realized that we’ve forgotten to set the right time on our dive computer!)

As an UWatec user, you’ll notice that there is no Daylight Savings setting or option on the dive computer. This is probably a good thing. The Daylight Savings rules world wide are varied and complicated and close to impossible to keep track of. If you’re in a place that observes daylight savings time, you’ll want to simply adjust your UTC offset. If you’re in Belgium in the summer time, you’re now “UTC +2:00”. If you’re on the Pacific coast of the USA, you’re now “UTC -7:00”. Your Mac has all the daylight savings rules built into it so you don’t have to tell it. But your dive computer has better things to do so you must tell it manually. Daylight savings is just a 1 hour change to the UTC offset.

This is actually a nice feature of these dive computers. But as it is with many things, it needs to be used properly or it may cause some headaches. If you have a bunch of dives on your UWatec that have the “wrong” time, Dive Log Manager/DiveLogDT has a special “switch” that will instead use your Mac’s time zone setting instead of the UTC offset when calculating the start time of the dive. Contact us on our support email address and we’ll give you directions.

Happy Diving and remember - "We've all got time enough to dive"!

New firmware for Heinrichs Weikamp Sport

Hello to HW Sport users on the Mac.

Dive Log Manager/DiveLogDT uses (regular) Bluetooth to download the Sport dive information into your logbook. In early August 2015, Heinrichs Weikamp introduced a new version of firmware for the Sport, version number 10.19. Unfortunately, this version of firmware has some Bluetooth timing problems when used with Mac hardware.

What you’ll notice is that downloading will encounter an error part way through the download. It won’t always be in the same place, but it will appear to be working fine initially, and then there will be around a 3 second “pause”, and then you’ll get a message saying there was an error downloading.

Heinrichs Weikamp has determined what the problem is, and there is now a new version of firmware available, version 10.20 and it is available here:

Also note that this problem will show up regardless of which logbook software you are using on the Mac. So this will show up with other 3rd party Mac based logbook software as well. Unfortunately, this problem will also make it difficult to upgrade the firmware to the new version on a Mac - you might have to find a PC in order to do the firmware upgrade.

Don’t hesitate to contact us or Heinrichs Weikamp if you have any questions.