Sensor and Performance

The Cooler Master MM311 is equipped with the PixArt PMW3325. According to specifications, the 3325 is capable of up to 5000 CPI, as well as a maximum tracking speed of 100 IPS, which equals 2.54 m/s. Through the software, an interpolated maximum CPI of 10,000 can be set. Out of the box, seven pre-defined CPI steps are available: 400, 800, 1200, 1600, 3200, 6400, and 10,000.

All testing was done on the latest firmware (1.4.0/1.5.1). 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 all over the place, which is a subpar result overall. In order to account for the measured deviation, adjusted and largely on-target steps of 400, 800, 1500, and 3000 CPI have been used for testing.

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 5000 CPI—to quickly gauge whether there is any smoothing, which would be indicated by any visible "kinks." While no such kinks are visible in either plot, several outliers are, which do not appear to be polling-related.


In order to determine motion delay, I'm looking at xSum plots generated at 1600, 5000, and 10,000 CPI. The line further to the left denotes the sensor with less motion delay. At both 1600 and 5000 CPI, I can measure a motion delay differential of roughly 4 ms. Remarkably, this continues to be the case even at the interpolated maximum of 10,000 CPI.

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. As can be seen in the plots, the sensor malfunctions around the 3.5 m/s mark. While this is above specifications, it may be regarded as insufficient.

Polling Rate Stability

For wired mice, polling-rate stability merely concerns the wired connection between the mouse (SPI communication) and the 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. While several outliers are visible, they do not show up periodically, which leads me to believe they are not caused by a desynchronization drift.


Second, I'm testing the general polling-rate stability of the individual polling rates in wireless mode. Running the MM311 at a lower polling rate can have the benefit of extending battery life. Aside from outliers at 1000 Hz, all available polling rates are 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. There is no jitter visible at 1600 CPI, while 5000 CPI shows minor jitter. This becomes more pronounced at the interpolated maximum of 10,000 CPI. Lastly, there is no lens movement.

Lift-off Distance

The MM311 does not allow for LOD adjustment. This is expected, as the 3325 lacks this functionality. The sensor does track at a height of 3 DVDs, but not at a height of 4 DVDs (3.6<x<4.8 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.

Using a debounce time of 1 ms, click latency has been measured to be 1.5 ms, with standard deviation being 0.37 ms. Using a debounce time of 2 ms, click latency has been measured to be 2.4 ms, with standard deviation being 0.38 ms. Finally, using a debounce time of 6 ms, click latency has been measured to be 6.4 ms, with standard deviation being 0.43 ms. Despite not being listed as Reflex compatible anywhere, I have been able to get Reflex readings, although they appear to be inaccurate, as the values are higher than they're supposed to be.

The main button switches were measured to be running at 1.934 V. I'm not aware of the voltage specifications of the Kailh GM 4.0 (60 M) switches, but find this voltage to be rather low.