( ( Vapor pressures ) ( ( are ( ( measured ( ( ( in torr ) or ) ( in ( millimeters ( of ( mercury ( -LRB- ( ( mm Hg ) -RRB- ) ) ) ) ) ) ) ) ( at ( a ( certain temperature ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Vapor) (NNS pressures)) (VP (VBP are) (VP (VBN measured) (PP (PP (IN in) (NP (NN torr))) (CC or) (PP (IN in) (NP (NP (NNS millimeters)) (PP (IN of) (NP (NP (NN mercury)) (PRN (-LRB- -LRB-) (NP (NNP mm) (NNP Hg)) (-RRB- -RRB-))))))) (PP (IN at) (NP (DT a) (JJ certain) (NN temperature))))) (. .)))
Vapor pressures are measured in torr or in millimeters of mercury (mm Hg) at a certain temperature.
(ROOT (S (NP (DT A) (NN torr)) (VP (VBZ is) (NP (NP (DT a) (NN unit)) (VP (VBN used) (S (VP (TO to) (VP (VB measure) (NP (NN pressure)))))))) (. .)))
A torr is a unit used to measure pressure.