If you take a look at the specifications, Endgame Gear doesn't mess around with low-quality components, and of course, the sensor isn't the exception either. The XM1 uses the top of the line PixArt PMW3389 optical sensor. This tracking unit is great; it provides raw and very responsive feedback without any filtering or unwanted acceleration. Unlike all other mice equipped with this sensor I've previously tested, the XM1 does not have smoothing above 1,850 CPI, which is a huge plus. You can turn it on with the standard values in the software (called ripple control), but it's absolutely unnecessary in my opinion as it only adds input lag. Huge props to Endgame Gear for disabling this completely unnecessary feature by default!
As for the sensor's technical specifications, the nominal maximum tracking speed and acceleration values are 450 IPS and 50 G respectively. The resolution can be set from 50–16,000 CPI in steps of 50 CPI, and available polling rate values are 1000, 500 and 250 Hz, which are respective nominal response times of 1, 2 and 4 ms. The lift-off distance is low as the sensor didn't track from a DVD in height (approx. 1.2 mm).
There is no jitter on the reasonable CPI steps, and I couldn't detect any unwanted angle snapping or sensor lens rattle, either.
CPI divergence is average, going into the positive. If you come from a mouse with positive divergence or none whatsoever, you may need to adjust your in-game sensitivity accordingly. Please note that this test is not 100% accurate, but resembles reality quite well.
Perfect Control Speed
Nominal perfect control speed (or PCS for short) is 450 IPS on this sensor, which translates to roughly 11.43 m/s. This is insanely high, and there's just no way of hitting it during intended (or even unintended) use. What this means is that the sensor can track even the fastest swipes without spinning out.
Speed Related Accuracy Variance
This test shows the sensor's accuracy at different speeds. You can see me doing a fast swipe to the right before I slowly slide the mouse back to its original position. There is pretty much no acceleration or deceleration here, or if there is any, it's due to human error.
Polling Rate & StabilityAll polling rate values are nice and stable, without any suspicious outliers or periodic drops.
Input Lag & Smoothing
As mentioned above, this mouse does not feature the PMW3389 smoothing issue, which increases at specific resolution steps starting with 1,900 CPI. Both 400 and 16,000 CPI track equally well, albeit I'd highly advise staying on a reasonable level. Contrary to what many may belief, very high CPI with lower in-game sensitivity won't be beneficial.
Click LatencyThis time around, I couldn't measure the click latency because the mouse has a rather unique analog method for switch registration. This means I cannot use my standard testing methods as they respond with a lot of 0.0 ms values, which is obviously false. The click latency of this mouse is supposedly lower than on any proper gaming mouse, an issue caused by its analog switch registering method.
Here's a full quote (from pzogel's review) of how this works from the mastermind behind Endgame Gear:
"(...) the Analog Key Sensing takes sample snapshots at an incredibly high speed (very much like a scope) and the bouncing of the switch is summed into this analog sampling signal and therefore the bouncing is transformed into a mathematical function rather than a digital bounce (0/1), thus eliminating the need to debounce altogether. This works similar to how different brightness levels are achieved for LEDs traditionally. LEDs are pulsed to achieve that, being always driven at their max brightness for small periods of time. The more times that happens the brighter the LED is perceived. Analog Key Sensing is the reverse of this and using true analog to actually see the 'brightness', i.e. the key level."
You can read more about this on the WO 2014/131699 patent's description page.