Sensor and Performance

The MSI Clutch GM51 Lightweight Wireless is equipped with the PixArt PAW3395. According to specifications, the 3395 is capable of up to 26,000 CPI, as well as a maximum tracking speed of 650 IPS, which equals 16.51 m/s. Out of the box, five pre-defined CPI steps are available: 400, 800, 1600, 3200, and 6400.

All testing was done on the latest firmware (1.00.30/1.00.17). As such, results obtained on earlier firmware versions may differ from those presented hereafter.

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 differ 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 consistently positive and very low, which is a very good result overall. Despite the 3395 supporting CPI adjustment in increments of 50, the UI only allows for increments of 100, limiting the degree of possible adjustment.

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 without special equipment, it is done by comparison with a control subject that has been determined to have consistent and low motion delay. In this case, the control subject is a Logitech G403, whose PMW3366 sensor has no visible smoothing across the entire CPI range. Note that the G403 is moved first and thus receives a slight head start.

Testing is restricted to 2.4 GHz mode as Bluetooth is not suitable for non-casual gaming applications.

Wired testing

First, I'm looking at two xCounts plots—generated at 1600 and 26,000 CPI—to quickly gauge whether there is any smoothing, which would be indicated by any visible "kinks." The second plot does show such kinks, indicating smoothing at that step. The GM51 Wireless also allows enabling MotionSync, though on the latest firmware, this is forcibly enabled regardless of the setting in the software.


Occasionally, things break regardless of MotionSync, resulting in numerous outliers.


Furthermore, an additional option called "Speed Shift" is available within the software, which essentially modifies the sensor framerate scaling curve. By default, "Gear 1" is active, which is supposed to be used for office work and non-competitive gaming. If set to the highest setting "Gear 3," SPI timing loosens slightly.


The different framerate scaling behavior impacts motion delay as well. This set of plots shows the start (first plot) and end (second plot) of an entire single motion (third plot) at 1600 CPI and Gear 1. Motion delay is higher at the onset of motion, and continually becomes lower throughout the motion.


The same motion at 1600 CPI and Gear 3 shows barely any difference.


Once smoothing, which is first applied at and above 9000 CPI, enters the picture, things are looking different. This set of plots once again shows the start (first plot) and end (second plot) of an entire single motion (third plot), though at 26,000 CPI and Gear 1. Note how motion delay increases throughout the motion, approaching 30 ms towards the end of it.


Compare the same motion at 26,000 CPI and Gear 3. The scaling is completely different, and so is motion delay at the start and end of the motion. In both cases, motion delay increases throughout the motion, but to a much greater degree at Gear 1.

Wireless testing

Once again, MotionSync is permanently enabled regardless of the setting within the software, resulting in fairly low SPI timing jitter.


Much like in wired mode, things occasionally break regardless.


Switching to Gear 3 has barely any effect.


The framerate scaling behavior largely matches wired mode. This set of plots shows the start (first plot) and end (second plot) of an entire single motion (third plot) at 1600 CPI and Gear 1. Motion delay is higher at the onset of motion, and continually becomes lower throughout the motion.


The same motion at 1600 CPI and Gear 3 does not show much of a difference, albeit a greater one than wired did.


Once smoothing, which is first applied at and above 9000 CPI, enters the picture, things are looking different. This set of plots once again shows the start (first plot) and end (second plot) of an entire single motion (third plot), though at 26,000 CPI and Gear 1. Note how motion delay increases throughout the motion, once again approaching 30 ms towards the end of it.


Compare the same motion at 26,000 CPI and Gear 3. The scaling is completely different, and so is motion delay at the start and end of the motion. In both cases, motion delay increases throughout the motion, but to a much greater degree at Gear 1.

Speed-related Accuracy Variance (SRAV)

What people typically mean when they talk about "acceleration" is speed-related accuracy variance (or 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 5 m/s, which is within the proclaimed PCS range and causes no observable sensor malfunction.

Polling Rate Stability

Considering the Clutch GM51 Lightweight Wireless is usable as a wired mouse as well, I'll be testing polling rate stability for both wired and wireless use.

Wired testing


All of the four available polling rates (125, 250, 500, or 1000 Hz) look and perform fine. This applies regardless of the set RGB lighting effect or illumination being enabled to begin with.

Wireless testing
For wired mice, polling rate stability merely concerns the wired connection between the mouse (SPI communication) and USB. For wireless mice, another device that needs to be kept in sync between the first two is added to the mix: the wireless dongle/wireless receiver. I'm unable to measure all stages of the entire end-to-end signal chain individually, so testing polling-rate stability at the endpoint (the USB) has to suffice here.


First, I'm testing whether SPI, wireless, and USB communication are synchronized. Any of these being out of sync would be indicated by at least one 2 ms report, which would be the result of any desynchronization drift accumulated over time. No off-period polls that would be indicative of a potential desynchronization drift are visible.



Second, I'm testing the general polling rate stability of the individual polling rates in wireless mode. Running the Clutch GM51 Lightweight Wireless at a lower polling rate can have the benefit of extending battery life. All of the four available polling rates (125, 250, 500, or 1000 Hz) look and perform fine. This applies regardless of the set RGB lighting effect or illumination being enabled to begin with.

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. There is no jitter visible at 1600 CPI. 6400 CPI lacks smoothing and shows minor jitter, whereas 26,000 CPI has a degree of smoothing and shows moderate jitter. Lastly, there is very minor lens movement.

Lift-off Distance

The Clutch GM51 Lightweight Wireless offers two pre-defined LOD levels. Using the "low" setting, the sensor does not track at a height of 1 DVD. Set to "high," the sensor does track at a height of 1 DVD, but not at a height of 2 DVDs (1.2<x<2.4 mm; x=LOD height). Keep in mind that LOD may vary slightly depending on the mousing surface (pad) it is being used on.

Click Latency

In most computer mice, debouncing is required to avoid double clicks, slam-clicks, or other unintended effects of switch bouncing. Debouncing typically adds a delay, which, along with any potential processing delay, shall be referred to as click latency. In order to measure click latency, the mouse has been interfaced with an NVIDIA LDAT (Latency Display Analysis Tool). Many thanks go to NVIDIA for providing an LDAT device. More specifically, the LDAT measures the time between the electrical activation of the left main button and the OS receiving the button-down message. Unless noted otherwise, the values presented in the graph refer to the lowest click latency possible on the mouse in question. If a comparison mouse is capable of both wired and wireless operation, only the result for wireless (2.4 GHz) operation will be listed.

In wired mode, click latency has been measured to be 5.3 ms, with standard deviation being 0.23 ms. In wireless mode (2.4 GHz), click latency has been measured to be 5.5 ms, with standard deviation being 0.37 ms.

The main button switches were measured to be running at 1.968 V. I'm not aware of the voltage specifications of the Omron D2FC-F-K (60 M) (China) switches, but 1.968 V does seem rather low to me.