1. Tsis tu ncua tshuaj xyuas qhov nqus ntawm qhov nruab nrab ntawm cov lim dej rau cov khib nyiab thiab kev puas tsuaj rau cov khoom siv lim dej;
2. Yog tias muaj cov khoom thaiv qhov chaw, lawv yuav tsum tau muab tshem tawm;
3. Yog hais tias qhov saum npoo ntawm cov khoom lim raug puas tsuaj loj, hloov cov khoom lim los yog hloov cov lim dej nruab nrab thiab rov nruab nws;
4. Thaum txhim kho cov lim dej nruab nrab, nws yuav tsum muaj kev sib khi zoo nrog lub npoo ntawm tus ncej kom tsis txhob muaj cua nkag;
5. Tsis txhob siv cov khoom hnyav los cuam tshuam rau saum npoo ntawm cov lim dej nruab nrab, thiab tsis txhob siv quab yuam los rub cov khoom siv lim dej ntawm cov lim dej nruab nrab;
6. Thaum txhim kho, qhov ntev ntawm lub hnab lim lub qhov ncauj yuav tsum yog perpendicular mus rau hauv av kom muaj kev lim dej ntxiv thiab lub sijhawm ua haujlwm ntawm huab cua.