There are a few things to unpack there. First of all, an A+ is the highest rating possible, and therefore is extremely tough to achieve—there is no A++ or any of that nonsense to water down the top grade. DisplayMate announced the OnePlus 7's newly earned grade on Twitter.
DisplayMate's in-depth Lab Tests of the OnePlus 7 Pro OLED Display have just been completed, earning our Highest A+ Display Rating. Our in-depth Display Shoot-Out will be published here on May 14.
— DisplayMate Tech (@DisplayMate) April 29, 2019
"DisplayMate's in-depth Lab Tests of the OnePlus 7 Pro OLED Display have just been completed, earning our Highest A+ Display Rating. Our in-depth Display Shoot-Out will be published here on May 14," DisplayMate said.
As it pertains to that, OnePlus CEO Pete Lau recently told The Verge that the display on the OnePlus 7 Pro variant costs three times as much as the displays on previous models. To be clear, it appears that DisplayMate's latest grade is for the non-Pro model, as the Pro variant is rumored to feature a fast 90Hz refresh rate.
The regular OnePlus 7 will not be expensive as the Pro version, but it is quickly becoming clear that OnePlus is willing to spend a premium on display technology for its next round of phones—the result is going to be best-in-class image quality on the OnePlus 7, and gaming-grade speed on the OnePlus 7 Pro.
"The display has Diamond Pixels and Sub-Pixel Rendering with 550 pixels per inch (ppi), providing significantly higher image sharpness than can be resolved with normal 20/20 Vision at the typical viewing distances of 10 inches or more for Smartphones, so the display appears perfectly sharp," DisplayMate said of the Galaxy S10.
DisplayMate also noted that the Galaxy S10 set several records, including for the highest full screen brightness for an OLED phone (804 nits) and highest peak brightness (1,215 nits).