Click the green flag to run the FPS counter. Running without screen refresh is not advised unless you have a VERY short "FPS Rolling Window," or you have a low "FPS Sample Limit." Setting this variable to 1 will allow you to "remove" the FPS cap that Scratch tends to run on (which is usually 30 FPS.) This variable does not work unless there is nothing visually updating on the screen, which means it probably won't do anything if you just add this FPS counter to an existing project, where there will almost certainly be something "happening" on screen at any given moment.
This FPS counter takes a "rolling estimate," in that it counts how many "frames" have occurred within a given period of time up to a certain threshold (which is set by the "FPS Rolling Window" and "FPS Sample Limit" variables), then extrapolates your FPS based on that information. Your FPS can be calculated as: (Number of Frames / (Newest Frame Time - Oldest Frame Time)) By adjusting the "rolling window", you can change how long a frame persists within the FPS calculator's "memory" before it's forgotten and deleted from the "FPS times" list. It also tells you how long it'll take for the FPS calculator to adjust to your current framerate if the project's average FPS suddenly changes. The "sample limit" allows you to control how many samples the FPS calculator can "memorize" to begin with, which helps prevents the list from being too large when the FPS is extremely high. Generally, increasing the rolling window makes the FPS counter adjust more gradually to framerate fluctuations, and provides a more accurate measurement of your "average" FPS. Decreasing the window can give you a better picture of your "current" FPS, but making it too short can give you extremely varied and inaccurate FPS measurements. The sample limit is there as a safety check, especially when you're trying to test this FPS counter without screen refresh.
