Hauv lub ntiaj teb kev lag luam e-lag luam uas hloov pauv sai sai, qhov ua tau zoo thiab tus nqi tsim nyog ntawm cov kev daws teeb meem xa khoom yog qhov tseem ceeb heev. Ntawm ntau yam kev xaiv ntim khoom muaj, cov ntawv xa ntawv poly tau tshwm sim los ua qhov kev xaiv nrov rau ntau lub lag luam. Cov ntaub ntawv ntim khoom no sib dua, ruaj khov, thiab yoog tau muab ntau yam txiaj ntsig uas tuaj yeem txhim kho cov txheej txheem xa khoom. Tsab xov xwm no tshawb nrhiav cov txiaj ntsig ntawm kev siv cov ntawv xa ntawv poly, txheeb xyuas leej twg yuav tsum siv lawv, thiab vim li cas lawv thiaj yog qhov kev xaiv zoo tshaj plaws rau cov kev xav tau xa khoom niaj hnub no.