A limited-use browser and related security system control access to content stored on a server computer linked to a network. The transmitter uses a half-rate precoder, half-rate non-linear modulation drive circuits and a multiplex modulator for generating duobinary modulation on an optical signal from which full-rate data can be detected without decoding. An aqueous solution in which zirconium salt or oxyzirconnium salt and polyvinyl alcohol are dissolved is neutralized by alkali. The user exercises by pulling the pull lines against the bias of the spring system. The data can be made available independent of location and for standard browsers via a web server integrated into the run-time system.