Technical requirements
Before beginning, I would like you to know about the timeline sketch:
|--x---x---x-x--x--x------> user event
The timeline sketch is a unique illustrative chart type that displays a series of events during a period. The left bar (|) stands for the time origin, representing the first update. The horizontal dash (-) moves with the time from left to right with an arrow > at the end. Each letter or number, such as x , indicates one event that happened in this timeline. In this book, we will use the timeline sketch to better understand a situation when multiple things happen simultaneously along the timeline.
