Many jump to the conclusion that kick cycles would be the answer here. Arm spans are far more accurate due to the physiology of human beings and that we have an approximate 1:1 ratio of our height to our arm spans.
Kick cycles are greatly affected by the water movement, the equipment we're using and even the style of kick each individual uses so are a good option for approximating larger distances but can never be as accurate as an individual's arm span equalling their height.
Having an environmental seal on your regulator's first stage may extend it's working life by protecting it from contaminants and of course, reduce the risk of it freezing up in cold environments or free-flowing in overhead environments.
I know I personally have Ice, Cavern and Cave Diving on my diving bucket list. What's on yours?
The Carotid-Sinus Receptors are part of a complex chain of nerves regulating arterial pressure and if the range they regulate exceeds a predetermined limit they signal for a reduction of that pressure by slowing the heart down.
This can be triggered by having a neck seal of your dry suit too tight or by wearing a tight hood while diving.
Using the eRDPml is required while completing the theory section of the PADI Instructor Exams so it's a great thing to become proficient at even if you use your computer to plan and dive with exclusively.
This question is pretty straight forward. Head to Dive Planning by scrolling through the Mode options on your PADI eRDPml - key in the depth and time information and record the pressure group designation to get the answer.
The catch in this question is that the object is in fresh water, not salt.
The constants to PADI Physics #exams are always listed on the top of the exam sheet so that makes it a lot easier to answer them.
The pressure change in fresh water is 0.097 ATM/m so if we divide the 20m depth by 0.097 we get 1.94 ATM. We then add the addition ATM from the air above the surface and get a total pressure of 2.94 ATA.
We can then multiply the 20% volume by the pressure change from the 20m/fw to the surface and we get the answer.