Excellent point. The latter. If you divide the motion of the bullet into a linear component and a rotational component, the additional friction drag only acts against the rotation. So the spinning bullet will slow its rotation over time, but the two bullets should have almost exactly the same speed.

It looks like "value of solar used" is cumulative, while the other measurements are monthly. This should be mentioned somewhere on the chart.

At a glance, it looks like the x-axis should be time, when in fact it's just the number of earthquakes. That's a bit misleading.