Tom qab txhim kho lub qhov rais, cov pob qij txha tsis zoo nyob nruab nrab ntawm qhov qhib thiab tus ncej. Yog tias lawv tsis ua tiav nrog cov khoom tsim nyog, tom qab lub sijhawm ua npuas ncauj mounting yuav vau, kub poob yuav nce. Thiab qhov pom ntawm lub qhov rais nws tus kheej tsis tas yuav tsis zoo. Qhov no yuav ua rau tag nrho cov kev xav ntawm tus tsim. Yog li ntawd, nws yog ib qho tsim nyog rau nruab qhov rais slopes. Cov txheej txheem no yuav muaj nyob rau hauv kab lus hauv qab no