Njerwa ndi bwino - zomangira zomangamanga, ndipo zimagwiritsidwa ntchito kwambiri m'minda yambiri. Monga limodzi la mafupa omanga, kufunikira kwa njerwa kumakulitsa pang'onopang'ono. Inde, njirayi ndiyosagwirizana ndi kugwiritsa ntchito makina opanga njerwa. Ndi ver
Mabatani a konkriti ndi malo ofunika omanga mu malonda omanga ndi kupanga maboti awa amafunikira kugwiritsa ntchito makina apadera monga makonzedwe opanga makina ndikutchinga makina. Makinawa amatenga gawo lofunikira