Sensor and Performance

The MSI Clutch GM51 Lightweight 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 (1.00.16). As such, results obtained on earlier firmware versions may differ from those presented hereafter.

Unless noted otherwise, I'll exclusively test the GM51 at 1000 Hz on this page. This is done both to provide the full picture and establish a baseline for testing polling rates higher than 1000 Hz, which follows on the next page.

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.


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." No such kinks are visible, indicating there not being any smoothing across the entire CPI range. The GM51 also allows enabling MotionSync, though on the latest firmware, this is always enabled regardless of the setting in the software.


In order to determine motion delay, I'm looking at xSum plots generated at 1600 and 26,000 CPI. The line further to the left denotes the sensor with less motion delay. While 1600 CPI has the GM51 in front, the reverse is true at 26,000 CPI, suggesting a motion delay differential of upwards of 1 ms between 1600 and 26,000 CPI. Due to MotionSync being permanently enabled, turning it off or on has no effect on motion delay.

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

All of the available polling rates (125, 250, 500, and 1000 Hz) show periodic bursts of off-period polls. This happens 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 shows minor jitter, whereas 26,000 CPI shows major jitter. This is in line with what to expect from a sensor lacking smoothing. Lastly, there is minor lens movement.

Lift-off Distance

The Clutch GM51 Lightweight 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.

Click latency has been measured to be 5.4 ms, with standard deviation being 0.12 ms. This applies regardless of the set polling rate.