Static Hedging with Uncertain Quantity and Departure from the Cost-of-Carry Valuation

A transmission control unit disclosed is used when an electronic device which is usually directly connected to a telephone line is used via a public telephone or the like. In this case, the transmission control unit is connected to a MODEM included in the electronic device, and a microphone and a speaker of the transmission control unit are brought to confront the speaker and the microphone of the telephone. When the transmission to the electronic device on the other end of the line is conducted, tone dialing is conducted to make a call and data is then transmitted. The thus transmitted data is converted by a converter of the transmission control unit so as to be transmitted to the telephone line connected to the other end of the line, while data from the electronic device on the other end of the line is transmitted and converted so as to be supplied to the MODEM. Therefore, a simply-structured and detachable transmission control unit enables data transmission and receipt via the public telephone simply by installing the transmission control unit.