You can have low bottle pressure on a full bottle, or high bottle pressure on a low bottle. I usually get pulsations when the bottle gets close to 2 pounds no matter how warm I have it so I've made it a point to leave that last 2 pounds in and save money on my refills. You want to see between 900 - 1100psi on the bottle with 1000 being pretty close to optimal. When the pressure starts to dip to around 600 on a bottle that's around 80 degrees you know it's getting to low for any real use and you're just wasting that last bit of nitrous. You should consume 4 pounds of nitrous for every 1 minute of use for every 100hp. This is a good rule of thumb to go by so you know about how much you're using and when it's getting time for a refill. | 
