Technical Atmosphere (at)

Technical Atmosphere is similar although not the same value as the standard atmosphere pressure unit (atm) and both have been used historically to relate a pressure value to multiples of atmospheric pressure. 1 Technical Atmosphere is defined as being exactly equal to 98,066.5 pascals.

The at pressure unit can be occasionally found on water resistant watches to indicate the maximum depth rating, particularly on European brands. However the unit has been largely phased out and the average atmospheric pressure is now mostly defined as 1 atm (101325 Pa) for weather and aviation or more commonly 1 bar (100,000 Pa) for industrial and general purposes.

Technical Atmosphere is sometimes written as ‘ata’ which is the short way of writing ‘at absolute’.