( Chemists ( often ( ( ( use ( as ( ( a unit ) ( of pressure ) ) ) ) ( ( ( the torr ) , ) ( which ( ( equals ( ( 1 mm ) ( of change ) ) ) ( in ( ( the height ) ( of ( ( the ( mercury column ) ) ( of ( a ( ( barometer or ) manometer ) ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (NP (NNS Chemists)) (ADVP (RB often)) (VP (VBP use) (PP (IN as) (NP (NP (DT a) (NN unit)) (PP (IN of) (NP (NN pressure))))) (NP (NP (DT the) (NN torr)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ equals) (NP (NP (CD 1) (NN mm)) (PP (IN of) (NP (NN change)))) (PP (IN in) (NP (NP (DT the) (NN height)) (PP (IN of) (NP (NP (DT the) (NN mercury) (NN column)) (PP (IN of) (NP (DT a) (NN barometer) (CC or) (NN manometer)))))))))))) (. .)))
Chemists often use as a unit of pressure the torr , which equals 1 mm of change in the height of the mercury column of a barometer or manometer.
(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.