My buddy and I are planning a shore dive. we're descending onto a very gradual slope that begins at 5 m/15 ft, so our descent and ascent will be a gradual part of swimming out and back underwater. we have similar cylinders filled to 2000 bar/3000 psi. We plan: - 50 bar/500 psi reserve
- 20 bar/300 psi for our safety stop
- to turn the dive when we've used 1/3 of the air available to use on the dive

This means we should head back when either of our SPGs read
A. 70 bar/800 psi
B. 145 bar/1900 psi
C. 157 bar/2270 psi
D. 170 bar/2500 psi