Reading Usable Help
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Gordon R. Meyer
Tricky interactive tutorials
One of the biggest challenges for any interactive tutorial is keeping the reader on the path you've defined. The software is typically operating in a "sandbox" environment, and is programmed to respond to specific user actions. If the reader decides to deviate from the tutorial, or gets too confused, the whole thing can easily fall apart. Careful planning and thought about remediation is a big part of the instructional design for any tutorial project.
The Try Ruby tutorial is a fun and interesting example. It gets several thing right, including the up-front statement of how much time the reader will be investing. It's worth spending 15 minutes to try it out, even if you're not interested in programming.