I didn't use any calibration tools when I began writing the review, since most end-users don't have them at their disposal. I first took the monitor out of the box, and ran a number of luminance, color fidelity tests uncalibrated. After that, I took a secondary set of recordings, this time with the monitor properly calibrated.
I tested the screen via DisplayPort at a 2560x1440 resolution and a refresh rate of 60Hz.
ASUS has opted to use flicker-free WLED backlighting offer with a peak-brightness of 346 candelas per square milimeter. That's most assuredly brighter than most screens, and it's more than enough for any kind of indoor use.
The thing is, most monitors don't have a uniform image across their entire surface, so in order to test its uniformity, I opted to take a look at its luminance. Whilst I worked with the review-sample, it's worth adding that these results only apply to the sample itself, and the values might differ between products from the same model. The reason I am actually performing this test is to see if there are some noticeable irregularities between the center and the corners, since that is usually indicative of an actual trend and not just individual issues.
For luminance uniformity, I set the screen-center at a luminance of 220cd/m2, and then took readings from its 8 surrounding regions. The end-result is a 13.6% variation from the darkest region, at the top-right edge of the screen. This is a very subtle variation, lower than ASUS' other two monitors I have reviewed, and it's unnoticeable to the naked eye.
Black Level uniformity is not far off, there are some bright spots in the bottom right corner, but the variation is only slightly noticeable.
Color rendition on the MX27AQ is nothing short of excellent. Even uncalibrated, the monitor has an average of 2.01 Delta-E, and once neatly calibrated at 200cd/m2, the screen has a stunning 1.82 average. These are some genuinely impressive performance figures for the monitor, though one should expect this kind of quality from an AH-IPS.
From my measurements, the contrast figures sit at around 944:1 - which is very close to the official 1000:1 static specs, which is always nice to see.
ASUS rates the optimal viewing-angles at 178 degrees, and my measurements show similar figures. The monitor has an optimal viewing angle at 177° of vertical range and 165° of horizontal. The color-shift is barely visible, noticeable on the horizontal axis, but almost unnoticeable on the vertical range.
Lastly, there's the power consumption of this monitor, and here ASUS' MX 27AQ is a surprising performer. It averages at about 36Watts, and consumes up to 51Watts with everything maxed up. In power-saving mode it only eats up about 0.5Watts.