Like the previous two assignments (Project-Based Math, Project-Based Math 2), Project-Based Math 3 focuses on multi-digit subtraction. Unlike the other two projects which focused on distance, this project was focused on time. It was well incorporated within a study of the Middle Ages that included studies of daily life and inventions. To get a sense of how much in advance certain events happened, it was important for the students to be able to calculate the difference between years. It was also valuable for them to understand how much (or how little, depending your perspective) time was between then and today.
As always, prior knowledge is essential. I would strongly urge that any project-based timeline assignment be housed in a humanities unit about whatever time period you focus on.
Here is the link to the Project-Based Math assignment about inventions and events in the Middle Ages. It also focuses on multi-digit subtraction, but this one has an awesome animation!