On loading you are given a menu choice of options, there is a Prestel mode, a terminal emulation mode compatible with Telecom Gold and the like, and a mode for sending and receiving ASC file text or programs down the phone from one Amstrad to another. The latter has its own error detecting system.
Unless you have a specific use for a modem that exceeds these capabilities, this package is an excellent value means of testing out a new hobby and provides you with an RS232 that will work on most applications as well. Worth 30 quid of anyone's money.