If each stage has a compression ratio of 7 to 1 , the compressor can output 343 times atmospheric pressure ( 7 x 7 x 7 = 343 Atmospheres ) . If each stage has a compression ratio of 7 to 1 , the compressor can output 343 times atmospheric pressure ( 7 Ã -- 7 Ã -- 7 = 343 atmospheres ) .