How much Gas is in the Gas Cylinder?

This is my computation of the amount of gas released as indicated by the Cylinder pressure Change.  It should be helpful in purging Headspaces, which requires  volumes of gas equal to FIVE times the volume of the Headspace in order to reduce the oxygen content down to about 0.21 percent.
Nitrogen Gas in a cylinder of 330 Cu Ft. Capacity, at 3000 psi
Pressure Pressure decrease Cu Ft.   Remaining  At STP Gas Remaining Gallons       At STP Cu Ft Released   At STP Gallons Released      At STP
3000 330.00 2475.00
2900 100 319.00 2392.50 11.00 82.50
2800 100 308.00 2310.00 11.00 82.50
2700 100 297.00 2227.50 11.00 82.50
2600 100 286.00 2145.00 11.00 82.50
2500 100 275.00 2062.50 11.00 82.50
2400 100 264.00 1980.00 11.00 82.50
2300 100 253.00 1897.50 11.00 82.50
2200 100 242.00 1815.00 11.00 82.50
2100 100 231.00 1732.50 11.00 82.50
2000 100 220.00 1650.00 11.00 82.50
1900 100 209.00 1567.50 11.00 82.50
1800 100 198.00 1485.00 11.00 82.50
1700 100 187.00 1402.50 11.00 82.50
1600 100 176.00 1320.00 11.00 82.50
1500 100 165.00 1237.50 11.00 82.50
1400 100 154.00 1155.00 11.00 82.50
1300 100 143.00 1072.50 11.00 82.50
1200 100 132.00 990.00 11.00 82.50
1100 100 121.00 907.50 11.00 82.50
1000 100 110.00 825.00 11.00 82.50
900 100 99.00 742.50 11.00 82.50
800 100 88.00 660.00 11.00 82.50
700 100 77.00 577.50 11.00 82.50
600 100 66.00 495.00 11.00 82.50
500 100 55.00 412.50 11.00 82.50
400 100 44.00 330.00 11.00 82.50
300 100 33.00 247.50 11.00 82.50
200 100 22.00 165.00 11.00 82.50
100 100 11.00 82.50 11.00 82.50
0 100 0.00 0.00 11.00 82.50
TOTALS: 3000 330.00 2475.00
Note: “At STP”  means  “At Standard Temperature and Pressure”,                                                      (20 Degrees C, and 1 atmosphere).
Note: “At STP”  means  “At Standard Temperature and Pressure”,                                                      (20 Degrees C, and 1 atmosphere).