[cameldrv]

I'm a little bit surprised to see this.

One thing I've observed working on many different types of software projects is that there exists a continuum between waterfall and agile/scrum, and one way of thinking of it is what the length of the sprint is. Waterfall is a single sprint the length of the product, spiral development is several sprints over the length of the product, and agile/scrum is sprints of a couple of weeks to a month.

The length of the sprint is simply the length of the planning cycle. What I've observed is that systems with certain characteristics, such as safety critical systems or systems that involve hardware that doesn't yet exist or is expensive or time consuming to test typically don't work with an agile/scrum planning cycle. If you want to deliver them in a reasonable time, complex and parallel requirements mean that you must plan things far in advance so that everyone is ready at the same time.