It’s an interactive program on the aircraft systems which I (and thousands of B737 pilots) use to supplement the Boeing Vol 2 (and other) manuals into one simple information guide. Essentially it brings the information from various parts of the manuals together in one place. It was created by a pilot with many years experience (and extensive knowledge) on type.
Essentially, you tap on the item and it will bring up details and schematics of the related system, which makes it a lot easier to understand.
It’s also great to focus on particular systems in preparations for the dreaded recurrent sim check. An example follows. In the app, you just tap on any light or switch to get a full rundown of the item. Beats going from book to book to book [emoji846]
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