## Posts Tagged ‘Statistics’

### SAC Rate Calculation

Sunday, April 3rd, 2011

Calculating the correct SAC rate for a dive sounds like a trivial and straightforward task, but if you want to do it right, you quickly get to some hurdles. SAC means “Surface Air Consumption” or for all German readers it’s the AMV = Atemminutenvolumen. The formula is indeed very simple:

MetricSAC = (TankPressureDiff * TanksizeLiter) / (Divetime * (AvgDepthMeter / 10 + 1))

ImperialSAC = ((TankPressureDiff / WorkingPressure) * TanksizeCuFt) / (Divetime * (AvgDepthMeter / 10 + 1))

So where is the problem, you think? Well, you have to consider:

• Is there a dive profile? If so, I can calculate the average depth and dive time from the profile. If not, the average depth must be entered manually. Before calculating the SAC rate, I have to check if all required data is available
• Metric or Imperial calculation?
• Double tanks? If so, multiply tank size with 2
• Now it’s getting complicated: Does the dive have multiple tanks? If not, we can calculate right away and that’s how it worked in the past. But now since Diving Log supports multiple tanks it’s getting a lot more difficult:

If a dive has multiple tanks, the only way to calculate a correct SAC rate for the whole dive is by calculating the separate rates for each tank and then the average. So now Diving Log will calculate the dive time and average depth for each tank by running through the dive profile. When completed, it will calculate based on these values the separate SAC rates for each tank and then the average rate for the whole dive. Look at this dive for example (all metric values):

Profile with multiple tanks

You can see the SAC rate for each tank in the tank window

So SAC rate calculation for dives with multiple tanks works only if a dive profile is available and when each tank is assigned to a part of the profile. Each dive can have up to 10 tanks. In a logbook with 1000 dives, each dive 10 tanks, Diving Log will have to calculate the SAC rate for 10000 tanks when creating the SAC rate chart below. Some dive computers record the profile with a 1 second interval, so you could imagine the amount of required calculations to create this chart:

SAC Chart

The improved SAC calculation will be available in the next beta.

### Diving Log 5.0 – Statistics

Tuesday, April 7th, 2009

The statistics window of version 5.0 is almost complete and I want to show you the changes and improvements. Beside some visual refreshments the “General” and “Additional” text statistics has been merged and moved to the top of the list.

Statistics

Some of the text items from the “Additional” panel were removed, because this data is already available as visual chart display, so it would be duplicate data (e.g. the depth range). The water- and entry type as long with the deco and repetive dive statistics will now be displayed as separate charts. To display this kind of data I’ve added 4 new chart types: Pie, Pie 3D, Donut and Donut 3D.

Pie 3D Chart

Donut 3D Chart

As you can see in the 2nd screenshot, the copy button has now a drop down menu where you can select the graphic format. The EMF format is best suited for pasting into Microsoft Word, because it is a vector format. The “save as file” function can now save the chart image as JPG, PNG, BMP and EMF.

The scrollable charts can now be zoomed to the full logbook range. If you have 1000 dives in your logbook you can zoom out until you see all dives. If more than 50 dives were displayed, the chart will automatically switch to either a line or an area chart type, because displaying more than 50 bar chart entries would cause bad performance. For the same reason the x-axis and the vertical grid lines will be hidden with more than 50 dives displayed.

SAC values of 175 dives

Every chart will remember its settings, so you can setup each chart as you want. The “Dive Type” chart will now display the dive types which you can edit in the logbook window (e.g. cave dive, night dive,…)