GTR in scuba diving stands for Gas Time Remaining. It's a crucial metric that helps divers manage their air supply and plan their dive effectively.
Understanding Gas Time Remaining (GTR)
GTR is typically displayed on dive computers, especially those with air integration. It estimates how much time a diver can remain underwater at their current depth and breathing rate before running out of usable air. This calculation considers:
- Tank Pressure: How much air is currently in the scuba tank.
- Breathing Rate (SAC/RMV): The diver's Surface Air Consumption (SAC) or Respiratory Minute Volume (RMV), which indicates how quickly they are using air.
- Depth: The current depth affects air consumption due to increased pressure.
Why GTR is Important
- Improved Gas Management: GTR allows divers to monitor their air supply in real-time and make informed decisions about extending or shortening their dive.
- Dive Planning: By comparing GTR with no-decompression limits (NDLs), divers can optimize their bottom time and ensure a safe ascent.
- Safety: Provides an immediate warning if air consumption is too high or if the dive is exceeding planned air reserves.
- Stress Reduction: Knowing the precise amount of time remaining based on gas supply reduces the stress of underwater navigation and air management, especially for newer divers.
Example of GTR Usage
Imagine a diver is at 60 feet and their dive computer displays a GTR of 25 minutes. This means, based on their current air consumption and tank pressure, they have approximately 25 minutes remaining at that depth before they need to begin their ascent. They can then compare this to their NDL to determine whether they can stay longer or if they need to start ascending.
GTR vs. Air Pressure
While air pressure (measured in PSI or BAR) is a direct reading of how much air is in the tank, GTR translates that pressure into a time estimate, making it easier for divers to understand and act upon the information. Air pressure alone doesn't account for depth or breathing rate.
