Sensor and Performance

The Xtrfy M4 is equipped with the PMW3389, which is one of PixArt's best optical sensors currently available. According to specifications, the 3389 is capable of up to 16,000 CPI as well as a maximum tracking speed of 400 IPS, which equals 10.16 m/s. Out of the box, it has no less than eight pre-defined CPI steps available: 400, 800, 1200, 1600, 3200, 4000, 7200, and 16,000.

CPI Accuracy

"CPI" (short for counts per inch) describes the amount of counts registered by the mouse if it is moved exactly one inch. There are several factors (firmware, mounting height of the sensor not meeting specifications, mouse feet thickness, mousing surface, among others) which may contribute to nominal CPI not matching actual CPI. It is impossible to always achieve a perfect match, but ideally, nominal and actual CPI should differ as little as possible. In this test, I'm determining whether this is the case or not. However, please keep in mind that said variance will still vary from unit to unit, so your mileage may vary.


I've restricted my testing to the four most common CPI steps, which are 400, 800, 1600, and 3200. As you can see, the deviation is very low (and consistent throughout), which is an excellent result.

Motion Delay

"Motion delay" encompasses all kinds of sensor lag. Any further sources of input delay will not be recorded in this test. The main thing I'll be looking for in this test is sensor smoothing, which describes an averaging of motion data across several capture frames in order to reduce jitter at higher CPI values, increasing motion delay along with it. The goal here is to have as little smoothing as possible. As there is no way to accurately measure motion delay absolutely, it can only be done by comparison with a control subject that has been determined to have the lowest possible motion delay. In this case the control subject is a G403, whose 3366 has no visible smoothing across the entire CPI range.


First I'm looking at an xCounts plot to quickly gauge whether there is any smoothing present, which would be indicated by any visible "kinks." Typically, the 3200 CPI plot would be expected to show such "kinks" given the 3389 usually has 32 frames of smoothing at and above 1900 CPI, which amounts to an added motion delay of roughly 4 ms at the lowest possible speed. This is not the case with the M4, however, which shows no signs of smoothing at 3200 CPI.



Second I'm looking at xSum plots generated at 400, 800, 1600, 3200, 4000, and 16,000 CPI to determine whether the 3389 in the M4 indeed does not have any smoothing. The line further to the left denotes the sensor with less motion delay. As you can see, motion delay is identical even at 4000 and 16,000 CPI, which confirms that the M4 indeed does not have any smoothing across its entire CPI range. We can infer from this that "ripple control" (which is the register that controls smoothing for the 3389) is not enabled within the M4's firmware.

Speed-Related Accuracy Variance (SRAV)

What people typically mean when they talk about "acceleration" is speed-related accuracy variance (or short SRAV). It's not about the mouse having a set amount of inherent positive or negative acceleration but about the cursor not traveling the same distance if the mouse is moved the same physical distance at different speeds. The easiest way to test this is by comparison with a control subject that is known to have very low SRAV, which in this case is the G403. As you can see from the plot, no displacement between the two cursor paths can be observed, which confirms that SRAV is very low.

Perfect Control Speed

Perfect Control Speed (or PCS for short) is the maximum speed up to which the mouse and its sensor can be moved without the sensor malfunctioning in any way. I've only managed to hit a measly 4 m/s (which is within the proclaimed PCS range), at which speed no sign of the sensor malfunctioning can be observed.

Polling Rate Stability

All three possible settings (125 Hz, 500Hz, and 1000Hz) look nice and stable.

Paint Test

This test is used to indicate any potential issues with angle snapping (non-native straightening of linear motion) and jitter, along with any sensor lens rattle. As you can see, no issues with angle snapping can be observed. As expected from a sensor without any smoothing, the higher CPI steps exhibit jitter and ripple. There is some minor jitter at 4000 CPI and some major jitter at 16,000 CPI. I'd consider the level of jitter at the latter step to be unusably high. That having been said, I struggle to see practical applications of such high CPI anyway. Furthermore, no sensor lens rattle is present.

Lift-off Distance

As far as I can tell, the M4 does not support adjusting LOD. This is unfortunate as the 3389 is fully capable of it. The only available (default) setting is very low as it doesn't track at a height of 1 DVD. It should be kept in mind, however, that LOD may vary slightly depending on the mousing surface (pad) it is being used on.

Click Latency

Since mechanical switches are being used for the buttons in most computer mice, debouncing is required in order to avoid unintended double clicks. Debouncing typically adds a delay (along with any potential processing delay), which shall be referred to as click latency. As there is no way to measure said delay directly, it has to be done by comparing it to a control subject, which in this case is the Logitech G100s. Click latency has been measured to be roughly +1.4 ms when compared to the SteelSeries Ikari, which is considered as the baseline with 0 ms. Please keep in mind that the measured value is not the absolute click latency. Comparison data comes from this thread as well as my own testing, using qsxcv's program.