this follow-on frame facility was exploited extensively by the implementation of "telesoftware" on prestel whereby computer programmes, notably for the bbc micro, were available for download from prestel. generally speaking, the first two or three frames acted as header pages. for example, one such programme was described on frame 70067a, and 70067b, while frame 70067c gave the number of subsequent frames containing the programme, and a crosscheck sum. special software enabled this crosscheck sum to be compared with a value calculated from the result of downloading all the required frames in order to verify a successful download. the actual telesoftware programme was contained from frame 70067d onwards, in this case for a further ten frames. in the event that the check failed it was necessary to download the entire programme again starting from the beginning.