under 1 atm vs at 1 atm

[Offroad]

Dear teachers

Which one of these read well?

The data was taken at/under 1 atm(@psi).

`Under` sounds better to me.

Many thanks

Offroad

[emsr2d2]

I don't know what it means but "at" and "under" mean two different things here. If the measurement was taken "at" 1 atm (whatever that means) then it's exactly "1". If it's "under" 1atm, then it's below 1 atm (so 0.99999 atm or lower).

[Offroad]

'At' it is then. 'Atm' is short for 'atmosphere', unit of pressure and equivalent to ~ 14.7 psi.

Very much appreciated.

Offroad