Njerwa ndi zida zomangira zodziwika bwino, ndipo zimagwiritsidwa ntchito kwambiri m'magawo ambiri. Monga imodzi mwa mafupa omanga, kufunikira kwa njerwa kukukulirakulira pang'onopang'ono. Inde, njirayi ndi yosasiyanitsidwa ndi kugwiritsa ntchito makina opangira njerwa. Ndi ver
Makina opangidwa mosamalitsa a Aichen - Semi - Makina opangira konkriti mosakayikira ndi nyenyezi yowala pantchito yomanga, ndikuchita bwino kwambiri komanso ntchito zosiyanasiyana, kupereka chithandizo cholimba komanso chodalirika cha v.