Sensor and Performance

The Xtrfy M42 is equipped with the PixArt PMW3389. 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, eight pre-defined CPI steps are available: 400, 800, 1200, 1600, 3200, 4000, 7200, and 16,000.

CPI Accuracy

"CPI" (short for counts per inch) describes the number of counts registered by the mouse if it is moved exactly an 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, deviation is low and exclusively positive. A very good result overall. Note: With the default out-of-the-box firmware, the 400 CPI step is actually set to 450 CPI internally. This bug has been rectified by a firmware update. The value above has been achieved using said firmware.

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. Note that the G403 is moved first and thus receives a slight head start.


First, I'm looking at two xCounts plots—generated at 1600 and 16,000 CPI—to quickly gauge whether there is any smoothing, which would be indicated by any visible "kinks." Typically, the 16,000 CPI plot would 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. As you can see, this is not the case here, which confirms that there is no visible smoothing across the entire CPI range. Like the M4, the M42 has the smoothing register usually enabled on the 3389 disabled. We also see some SPI timing variance, although it's slightly improved compared to the M4.


In order to determine motion delay, I'm looking at xSum plots generated at 1600 and 16,000 CPI. The line further to the left denotes the sensor with less motion delay. Neither 1600 nor 16,000 CPI show any difference in motion delay, which merely confirms the results from above.

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 no sign of the sensor malfunctioning can be observed.

Polling Rate Stability

All three available polling rates (125 Hz, 500 Hz, and 1000 Hz) look nice and stable. Polling stability is unaffected by any of the available RGB settings.

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. No jitter is visible at 1600 CPI. 7200 CPI shows moderate jitter, and 16,000 CPI shows high but not excessive jitter. This is in line with what to expect from a sensor that lacks any sort of smoothing. Lastly, there is no sensor lens movement.

Lift-off Distance

The M42 lacks any options for LOD adjustment. This is unfortunate as the 3389 is fully capable of it. At the default (and only) setting, the sensor does not track at a height of 1 DVD (<1.2 mm). Keep in mind 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 +3.8 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.