I was looking at this graph and wondering what the value of the graph would be before the engines turn on. Should it be 1 g-force or 0 g-force? (the "force" in g-force being a misnomer as it is a measure of acceleration, not force) Below are arguments for each: Why it should be 1 g-force: We experience 1 g-force of acceleration on earth's surface. The astronauts would also experience 1 g-force before the engines turn on. Why it should be 0 g-force: The acceleration of the rocket (in m/s^2) is clearly 0 while the rocket is still on the ground. 0 m/s^2 corresponds to 0 g-force. Which is the correct interpretation? Or is this just a problem of choosing your zero? In that case what is the convention?