computer psi safety margin and sac rate?

I have my psi safety margin set to 300 psi so that if in the event that I did something extremely foolish and allowed myself to completely empty my tank on a dive I still have the capacity to ascend at a safe rate and complete any safety stop, then surface with 300 psi still in my tank. I stick to the dive plan and this situation would never intentionally happen and only exists as a safety feature but my question is.....When i am figuring my sac rate for a dive has this 300 psi been somehow subtracted by my computer? When i look at my ending pressure versus my starting pressure should i be adding 300 to get my true sac rate. I probably should have compared my computer to my redundancy pressure gauge to see if there was any difference but alas i did not but certainly will on my next dive.
I welcome any imput.

300 is way too little IMHO, RBT time for say AL80 and 60ft is approx 900psi. It takes into account 2 people at a higher than average SAC rate into account. So they can surface and make the stop. I believe that's what you have to set as your safety margin. I used to set 1000psi on my computer which was good to 80ft on my HP100 My computer was calculating "safe minutes" to that reserve. but SAC rate itself does not depend upon you reserve. It's just that Surface Air Consumption Rate and calculated for 1 minute.

A lot depends on the planed depth. 300 may be a min. EOD planed reserved for a shallow 30'-60' warm water dive but it not enough for a +60' cold water dive.

But yes, make your plan to include your safety margin reserves.

Robertcrockett:

I have my psi safety margin set to 300 psi so that if in the event that I did something extremely foolish and allowed myself to completely empty my tank on a dive I still have the capacity to ascend at a safe rate and complete any safety stop, then surface with 300 psi still in my tank.

Click to expand...

If you completely empty your tank, your tank is empty! All the computers that I am aware of the "safety margin" is taken into account when the computer calculates how many minutes of gas you have left, e.g., if it says you have five minutes of gas remaining, that's five minutes until you reach your "psi safety margin."**

Robertcrockett:

has this 300 psi been somehow subtracted by my computer? When i look at my ending pressure versus my starting pressure should i be adding 300 to get my true sac rate.

Click to expand...

Beginning and ending pressure are just that; the psi margin does not influence those numbers.

**for the Oceanic VT3 computer, for example, Air Time Remaining "is the time you can remain at the present Depth and still safely surface with the Tank Pressure Reserve that you selected during setup."

How does this work?

Does your computer hide 300PSI from you? If a full fill is 3000PSI, will it read 2700 (and 0 when it's actually at 300)?

Or does it simply instruct you to ascend in such a way that you will have 300 when you reach the surface?

Your SAC rate must be calculated using the amount of gas you actually consume. If you are unsure what the computer is doing, read the manual.

I use the Aeris Epic AI and according to the manual it constantly adjusts your air time remaining based calculations of your current depth, breathing rate, cylinder pressure, ascent time, and decompression status to tell you exactly how much time you can remain underwater. The Epic monitors no decompression status, oxygen accumulation and breathing gas consumption rate. The computer displays whichever of these that currently allows less time. When your air time remaining reaches zero you still have enough to reach the surface including safety stops with the set air reserve you chose. So tank pressure remains constant across both the computer and pressure gauge. No air is *hidden* or subtracted, your dive time is simply constantly updated based on the above factors and it figures in that you want to be able to surface with X amount of PSI.
Sorry to sound like such a newb but my wife had my vehicle which contained my dive computer and manual. I had been trying to mull this over in my head for several days but couldnt get access to my manual so I tried scubaboard but without anything to reference I had it all confused.
Thanks for the help