The attopascal is a multiple of the unit bit for Pressure. The prefix atto (symbol a) is defined in the International System of Units (SI) as a multiplier of 1.0 × 10-18 (1 quintillionth, trillionth, short scale), and therefore 1 attopascal = 1.0 × 10-18 pascals = 0.000000000000000001 pascals. The attopascal has the unit symbol aPa.
torrs
The torr (symbol: Torr) is a unit of pressure based on an absolute scale, now defined as exactly 1/760 of a standard atmosphere. Thus one torr is exactly 101325/760 pascals (~133.3 Pa).