Etching is dissolving and shaving technology. In wet etching which utilizes chemical reactions, thickness adjustment of high precision crystal units and frequency adjustment of AT oscillators are available. Etching is rather than an indivisual technology, often used in combination with the previous process of photolithography, and and is able to conduct shape processing of highly productive tuning-fork crystal units as well as Si etching through dry etching that uses reactive gas. There are also other etching methods, including micro blast processing that shaves materials by using abrasive. They correspond to a wide variety of purposes.