A mini controller has an intelligent central unit; a storage unit, an operating unit and a display unit. A point iteration technique provides direct calculation of low order digits of winding counts without use of complex intervals. Decryption and identification of the next server occurs in a sequential manner in which the path is known only to the sender. This system allows the utility company to transmit the reading of utility consumption by a consumer without the use of telephone lines. An interposing etch stop layer is used when the same material composition is used to form both the spring metal and stress-balancing layers. It is possible to make the color conversion characteristic to obtain color reproduction closer to the ideal color reproduction according to a standard, and the color conversion characteristic can be determined in a short time.