( We ( ( measure ( ( ( ( air pressure ) ( in millibars ) ) , ) ( using ( ( an instrument ) ( called ( a barometer ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VB measure) (NP (NP (NN air) (NN pressure)) (PP (IN in) (NP (NNS millibars))) (, ,) (VP (VBG using) (NP (NP (DT an) (NN instrument)) (VP (VBN called) (NP (DT a) (NN barometer))))))) (. .)))
We measure air pressure in millibars, using an instrument called a barometer.
(ROOT (S (NP (NNP Millibar)) (VP (VBZ is) (NP (NP (DT the) (NN unit)) (VP (VBN used) (S (VP (TO to) (VP (VB measure) (NP (NN air) (NN pressure)))))))) (. .)))