Frequently Asked Questions
My Download Is Missing Dives
We get asked this question a lot: Why can't I download all of my dives? I've done more, I can see them on the dive computer, but MacDive doesn't work??
Well, there could be a number of reasons to explain what you're seeing. Generally speaking if you do not see an explicit error message indicating some kind of failure, there's probably nothing wrong, and it may simply be that your device is full. Yes, even if you can see them on the dive computer. Read on for a little more information about how this stuff works.
So, what's the story?
Dive computers typically have a very limited amount of memory that they can use to store dives. The amount of dives they can hold varies from device to device based on things like how much memory they actually have, how efficient they are at storing dive data, and how often they record it.
Often dive computers have a configurable sample rate. This is the rate at which they record information. Usually it is in the 10-30 second range. That is to say, every 10-30 seconds they record the depth, temperature, air, and other bits of information, while you're diving. The more frequently this happens, the more memory the dive will consume on your device. And as you can guess, that means you can store less dives overall before the device is full.
First In, First Out
The most common way that dive computers store dives internally is like a ring. As you make more dives, the computer moves around the ring, saving them. When it gets full, you're back at the start! So, the earliest dive gets overwritten, and back around the ring we go, replacing older dives as newer ones are saved.
But MacDive is wrong, my computer says I've done 500 dives!?
Often dive computers will record the total number of dives you've made with them. They don't record any further information, just a running total, in addition to the latest profiles that are still available. This doesn't mean they are all available to download. More likely than not, the earliest ones have long been overwritten.
But MacDive is wrong, I can see the dives on my dive computer!?
This can certainly be confusing. Some models of dive computer really have two parts to how they store dives. The first part is really simple. It consists of things like the date, the maximum depth, the dive number, etc. It only has a few little bits of information that take up a tiny amount of memory. You can think of this very much like a table of contents.
The second part is the actual profiles. This will take up a lot more memory, and as discussed above, can take more or less space based on the sample rate, the actual model of computer, etc.
In one particular example, the user manual for a device states that it can store 24 dives. Of course, this is slightly misleading. What it means is that the "table of contents" can hold the basic details of 24 dives. This won't change - as soon as you do the 25th dive, it will replace the 1st dive, and so on. The actual profiles, however, vary based on the length of the dives, the sample rate, etc. In one case a user had only the last four dives available, due to the very high sample rate.
So yes, there are cases where you can scroll through the main details of some dives that MacDive won't download.
So what can I do?
The best thing to do is to download as often as you can to avoid filling up your dive computer and missing some dives. Obviously this depends on many of the factors discussed above.
Sometimes, however, you may be away diving and not have the ability to download. If your device has a configurable sample rate, you may be able to decrease it (use a higher number, for example 30 seconds instead of 15). This may allow you to store more dives, at the cost of slightly less samples per dive.