Updated it so that rerunning or cancelling the benchmark doesn’t break or mess up the results.
I’m not sure if this is the problem but GameMaker averages the number over the last second or two so, so if the simpler tests are too fast it’ll churn through it before the figure has time to correct itself after the lag of spawning all of the geometry. I added a five-second delay before the start of the first test which will hopefully be enough to get past that.