( ( ( ( We ( normally ( count ( the day ) ) ) ) - ) ( ( the time ) ( it ( takes ( Earth ( to ( ( ( ( rotate once ) ( on ( its axis ) ) ) - ) ( as ( ( the ( smallest unit ) ) ( of ( calendrical time ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (PRP We)) (ADVP (RB normally)) (VP (VB count) (NP (DT the) (NN day)))) (: -) (S (NP (DT the) (NN time)) (NP (PRP it)) (VP (VBZ takes) (S (NP (NNP Earth)) (VP (TO to) (VP (VB rotate) (ADVP (RB once)) (PP (IN on) (NP (PRP$ its) (NNS axis))) (: -) (PP (IN as) (NP (NP (DT the) (JJS smallest) (NN unit)) (PP (IN of) (NP (JJ calendrical) (NN time)))))))))) (. .)))
We normally count the day - the time it takes Earth to rotate once on its axis - as the smallest unit of calendrical time.
(ROOT (S (NP (NNP Earth)) (VP (VBZ rotates) (PP (PP (IN on) (NP (PRP$ its) (NNS axis)) (ADVP (RB once))) (CC times) (PP (IN in) (NP (CD one) (NN day))))) (. .)))