physical vs logical pixels #specctr_points_vs_pixels
images - Are pixels in Photoshop logical or physical? - Graphic Design Stack Exchange
What's a Pixel? - Appway Developer
iPhone 6 Screens Demystified
A pixel is not a pixel is not a pixel - QuirksBlog
When the zooming factor is exactly 100%, one CSS pixel equals one device pixel (though the upcoming intermediate layer will take the place of device pixels here.) The image below depicts that.
css - what exactly is device pixel ratio? - Stack Overflow
The reason that CSS pixel ratio was created is because as phones screens get higher resolutions, if every device still had a CSS pixel ratio of 1 then webpages would render too small to see.
More about devicePixelRatio - QuirksBlog
devicePixelRatio is the ratio between physical pixels and device-independent pixels (dips) on the device. devicePixelRatio = physical pixels / dips