Triangle: Sum of Interior Angles

A B Cron
If you were stranded on a desert island and had to take the GED test, there is the one rule about triangles you should bring along. Can you discover this rule? You can move the labels α, β, and γ with your mouse to read.
Make a table on your paper similar to the one above. Copy down the values of each angle α, β, and γ. Use your calculator to find the sum (remember technology tools round off values, so the sum should be and integer.) Can you write the rule?