You can see the bolt snap hanging off the hose in the left picture:
A mod-S drill is a mock-deploy. While you're sitting geared up, have the primary reg in your mouth and take a few breaths from it. Then, deploy it as if there's an OOA diver in front of you. With your left hand, insert the necklaced backup reg into your mouth and take a few breaths from it. Free the entire length of the long hose from underneath your right arm. Then, stow everything back the way it was.
Performing this drill fully ensures that your tank valve is one, that your regulators are functioning, that your long hose is not trapped under your backup hose or anything else, that your backup is necklaced around your neck, and that you've routed the long hose correctly for a clean deploy.
![spg-attachment.jpg](http://www.gue.com/files/page_images/equipment/Config/spg-attachment.jpg)
A mod-S drill is a mock-deploy. While you're sitting geared up, have the primary reg in your mouth and take a few breaths from it. Then, deploy it as if there's an OOA diver in front of you. With your left hand, insert the necklaced backup reg into your mouth and take a few breaths from it. Free the entire length of the long hose from underneath your right arm. Then, stow everything back the way it was.
Performing this drill fully ensures that your tank valve is one, that your regulators are functioning, that your long hose is not trapped under your backup hose or anything else, that your backup is necklaced around your neck, and that you've routed the long hose correctly for a clean deploy.