▁on ▁the ▁right , ▁the ▁intensity ▁changes ▁of ▁the ▁pe aks ▁at ▁ 1 0 ▁and ▁ 3 0 ▁are ▁related ▁and ▁the ▁intensity ▁of ▁the ▁peak ▁at ▁ 1 0 ▁and ▁ 3 0 ▁changes ▁in ▁the ▁opposite ▁direction ▁( negative ▁cross - pe ak ▁at ▁( 1 0 , 3 0 )). ▁The ▁same ▁is ▁true ▁for ▁the ▁pe aks ▁at ▁ 2 0 ▁and ▁ 4 0 . ▁ ▁Det erm ining ▁the ▁sequence ▁of ▁events ▁Most ▁important ly , ▁with ▁the ▁sequ ential ▁order ▁rules , ▁also ▁referred ▁to ▁as ▁N oda ' s ▁rules , ▁the ▁sequence ▁of ▁the ▁intensity ▁changes ▁can ▁be ▁determined . ▁By ▁carefully ▁interpre ting ▁the ▁signs ▁of ▁the ▁ 2 D ▁synchron ous ▁and ▁asynchronous ▁cross ▁pe aks ▁with ▁the ▁following ▁rules , ▁the ▁sequence ▁of ▁spectral ▁events ▁during ▁the ▁experiment ▁can ▁be ▁determined : ▁ ▁if ▁the ▁intens ities ▁of ▁the ▁bands ▁at ▁x ▁and ▁y ▁in ▁the ▁dataset ▁are ▁changing ▁in ▁the ▁same ▁direction , ▁the ▁synchron ous ▁ 2 D ▁cross ▁peak ▁at ▁( x , y ) ▁is ▁positive ▁if ▁the ▁intens ities ▁of ▁the ▁bands ▁at ▁x ▁and ▁y ▁in ▁the ▁dataset ▁are ▁changing ▁in ▁the ▁opposite ▁direction , ▁the ▁synchron ous ▁ 2 D ▁cross ▁peak ▁at ▁( x , y ) ▁is ▁negative ▁if ▁the ▁change ▁at ▁x ▁mainly ▁preced es ▁the ▁change ▁in ▁the ▁band ▁at ▁y , ▁the ▁asynchronous ▁ 2 D ▁cross ▁peak ▁at ▁( x , y ) ▁is ▁positive ▁if ▁the