Folks,
Joe is correct here AFAIK. For instance, in aviation we are taught and use 1.013 for standard atmosphere, not 1.000, and this is an international standard.
Also, the formula is: Depth
in ata times the fraction of the gas. The conversion in Imperial measurement (Yes, guys, I admit metric works more easily.) is:
Depth in fsw divided by 33, result plus 1 = depth in ata.
Just my ppO2's worth.
(DISCLAIMER: I am not a mathematician nor an engineer, nor do I play either on TV. I am a pilot, and we generally use fancy computers to get our answers these days!!
)