HUD modes are viewed as when the person behind the HUD has different indicators to show them what information is needed on screen. For instance, the first mode is a dormant mode that shows the usual HUD screen and doesn't change. Mode two may change a little but doesn't differ much. Modes 3 + 4 usually tell you about a threat or give a warning of some sorts (easily seen in movies).
HUD Modes Analysis
Design Planning Exercise
With the help of Google Sheets, I've curated a Gantt chart similar to what Ash mentioned in our training exercise. I did my chart over the progression of this class and my goal completion date.