Sensor and Performance

The Fantech Helios XD3 V2 is equipped with the PixArt PAW3370. According to specifications, the 3370 is capable of up to 19,000 CPI, as well as a maximum tracking speed of 400 IPS, which equals 10.16 m/s. Out of the box, six pre-defined CPI steps are available: 400, 800, 1200, 2400, 5000, and 19,000.

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 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 exclusively positive, highly consistent, and somewhat high, which is an average result overall. In order to account for the measured deviation, adjusted steps of 400, 750, 1550, and 3050 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, 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.

Wired Testing

First, I'm looking at two xCounts plots—generated at 1600 and 19,000 CPI—to quickly gauge whether there is any smoothing, which would be indicated by any visible "kinks." Neither plot shows any, which strongly suggests there not being any smoothing. As an aside, SPI timing jitter is fairly low.


In order to determine motion delay, I'm looking at xSum plots generated at 1600, 19,000, and 19,000 CPI with ripple control enabled. The line further to the left denotes the sensor with less motion delay. Neither 1600 nor 19,000 CPI show any motion delay differential, which confirms that there is no smoothing across the entire CPI range. Upon enabling smoothing, a motion delay differential of roughly 2 ms is present at 19,000 CPI.

Wireless Testing

Not much changes when running the Helios XD3 V2 in wireless mode as SPI timing jitter and general tracking are virtually on the same level as when wired. However, the occasional outlier creeps in at times, especially after changing the CPI level:


A similar behavior could be observed on the AQIRYS T.G.A., which shares the MCU.


Once again, 1600 and 19,000 CPI are tested. Keeping the motion delay differential in wired mode established above in mind, I can measure a wireless motion delay of roughly 1 ms.

Speed-related Accuracy Variance (SRAV)

What people typically mean when they talk about "acceleration" is speed-related accuracy variance (or SRAV for short). 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 shows no sign of the sensor malfunctioning.

Polling Rate Stability

Considering the Helios XD3 V2 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 available polling rates (125, 250, 500, and 1000 Hz) look and perform fine, and polling stability is unaffected by any RGB lighting effect.

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. I'm unable to detect any periodic off-period polls that would be indicative of a desynchronization drift.


Second, I'm testing the general polling-rate stability of the individual polling rates in wireless mode. Running the Helios XD3 V2 at a lower polling rate can have the benefit of extending battery life. Only 1000 Hz is fully stable, whereas all the other polling rates exhibit periodic outliers. Polling stability is generally unaffected by the RGB lighting effects but for a single exception:


Steady, despite being the simplest effect of them all, introduces major instability and thus is best avoided.

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. 19,000 CPI shows major jitter, which is due to the lack of smoothing. Upon enabling smoothing, jitter is visibly lessened. Lastly, there is very minor sensor lens movement.

Lift-off Distance

The Helios XD3 V2 offers two pre-defined LOD levels. At the "1 mm" setting, the sensor does not track at a height of 1 DVD (<1.2 mm). Using the "2 mm" setting, the sensor does track at a height of 1 DVD, but not at a height of 2 DVDs (1.2 mm<x<2.4 mm, with x being 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, mechanical switches are being used for the main buttons, which require debouncing 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 outside of using a USB analyzer, it has to be done by comparing it to a control subject, which in this case is the ASUS ROG Chakram Core. The test setup involves wiring the NO pin of one of the main button switches of the test subject to one of the control subject, and qsxcv's program is used to measure the relative delay between them. Doing so is only possible if the devices in question are plugged into the PC through a wired connection. The Zaunkoenig M2K has been posited as the baseline for being within 0.1 ms of the possible minimum click latency of a high-speed device and within 0.2 ms of a hypothetical absolute minimum. As such, the resulting values may be considered quasi-absolute.

Using the 0 or 1 ms setting, click latency has been measured to be roughly +2.7 ms, with standard deviation being 0.48 ms. Scaling is linear.

The main button switches were measured to be running at 3.31 V. I'm not aware of the voltage specifications of the Kailh GM 8.0 (80 M) switches, but consider it likely these are running within specifications.