Increasingly, when measuring the performance of a PC in games, one can notice the indicators “0.1% Low” and “1% Low”. Most inexperienced users do not attach any importance to this and, in the old fashion, only look at the average FPS. In fact, these indicators are very important and worth paying attention to. And that’s why.
What is Average FPS and Frame Time
The time it takes to draw one frame is called Frame time or “frame time”. It is measured in milliseconds, but usually the frame rate is used, which indicates the number of frames rendered per unit of time. The frame rate is measured in the number of frames per second – Frames per second, or FPS.
The main unit used to measure performance is the average FPS (AVG FPS) over the entire period of time. The average FPS is found by the formula FPS = n / t, where n is the number of frames rendered for the entire time, and t is the time of the test. The average FPS has a drawback that does not allow it to be the only unit of measurement in benchmarks.
AMD Ryzen 5 3600 OEM 17 899 Processor *
0.1% minimum and 1% low FPS
When measuring FPS, its average is not an accurate value, so attention should be paid to others – 1% low and 0.1% minimum FPS. In our case, it is important to understand that the time it takes to draw a frame depends on its complexity. During the game, there may be cards with a large number of objects and NPCs in the player’s field of view, which will take more time to render. Such frames can linger on the screen, as a result of which the picture can freeze and spoil the impression of the game. The problem with the average FPS is that when measuring the time of the “long” frames is averaged with the “fast” ones, so information about the first is lost.
For example, 30 frames were rendered per second with the following rendering time in ms:
In this case, the average FPS is 30 frames per second, and the average frame render time is 33.3 ms. The overall picture is pretty good, but if you take a closer look, you can see four frames, the rendering time of which is two or even three times the average. As mentioned earlier, when calculating the average frame rendering time and average FPS, “long” frames are lost against the background of “fast” ones, as a result of which the values are inaccurate.
It was decided to somehow supplement the average FPS values in order to better describe all the frames.
There is such a concept as a percentile, from English – percentile (in Russian, the percentile or percentile is more common). In our case, this can be interpreted as a value below which a certain percentage of data from the total set is located. Our 99th percentile is the value below which 99% of the total data is. And, if it is equal to 90 ms, then 99% of the frame times from the example are less than 90 ms, and 1% is greater than or equal to this number.
Benchmarks use 99.9 and 99 percentiles by convention. Since FPS is usually used as the unit of measurement, in this case the inverse 0.1- and 1-FPS percentiles are used. They are popularly called 0.1% minimum and 1% low FPS. Usually, these values are below the average FPS, as this is the piece of data that describes rare game events with a large number of objects. This suggests that the complexity of the frames in the scene is not constant. It’s bad only when 0.1% minimum and 1% low FPS “sink” to a non-playable level, as a result of which the picture starts to jitter. True, it is statistically impossible to assess this unplayable level – it is different for everyone due to the peculiarities of the human eye and the habits of the gamer.
Mathematical explanations for the disadvantages of average FPS (for the curious)
There is a mathematical relationship between frame time and frame rate: the FPS value after rendering the frame – instantaneous FPS – inversely to the rendering time of this frame:
Since frame time is usually measured in milliseconds and frame rate in units per second, the above formula would look like this:
For example, a frame was rendered in 25 ms, then it turns out that the instantaneous FPS at the end of its rendering was equal to 1000/25 = 40 FPS.
As mentioned earlier, the average FPS is found using the formula FPS = n / t. In addition to it, the average FPS can be found as follows:
That is, the average FPS is the inverse of the average frame time. This is confirmed by the fact that the benchmark time is equal to the sum of the rendering time of all frames:
But why is the average FPS not accurate enough? This is because the average FPS is not the arithmetic average of the instantaneous FPS:
To confirm this, we present one of the above formulas:
The values of the average FPS and the average value of the instantaneous FPS will be equal only if all frames were drawn at the same time intervals – t1 = t2 = t3 = t-nth = t, which is practically impossible in practice. This is the main disadvantage of the average FPS.Outcome
Average FPS is far from ideal, and when measuring system performance in games, you should not focus only on it. 0.1% minimum and 1% low FPS on the contrary are very important units of measurement. In simple terms, they show the largest FPS drawdowns during the test, spoiling the overall impression of the game.