The RBT on the Galileo keeps track of how long your gas is going to last in real time based on your depth, your breathing rate and how much gas you have in your cylinder. As you ascend,the RBT will increase as long as your breathing rate is the same and you are not going through your gas faster than you are ascending. We recommend hitting your Max. depth and coming up nice and slow doing a multi-level dive.
We use the Galileo Sol in our training programs. We recommend that when your RBT or No Stop time reaches 10 ( mins ) or more, you start a very slow ascent. Both RBT and No Stop should increase. If your RBT, goes below 10 mins., continue your ascent but a faster rate.
It is up to you to do safety stops as you ascend. We recommend that you use the rule of thirds even for rec. diving. You should have 1/3 of your cylinder to do your safety stops. We suggest 1 -3 minutes at about 40 ', 3 - 5 minutes around 25' and 5 minutes or so around 15'. Of course, keep your eyes open for the dolphins, manta rays, turtles and anything else that likes to frolic in the shallows.
As CPH, mentioned, it is up to you to decide how much gas that you want to end up with on the surface. At that time your RBT will hit zero.
We recommend that you set your reserve at around 600 psi for a 3000 psi tank. The more adventurous the dive the higher you set your reserve. For tec diving 1000 psi. For a very shallow dive under your boat with no current you may set it lower that 600 PSI. It is up to you.
We just returned from Bonaire with a very enthusiastic group of newer divers. Their goal was to have at least an hour bottom time on each dive. By using the RBT and downing loading their dives, they all excended their goal.
Good Luck and Good Diving!