Here is a link by paintcodeapp going over the different device sizes for apple devices.
It shows a simple mathematical relationship between points, pixels, and physical pixels.
When I am setting say the width of a picture in CSS like this:
img {
width: 100px;
height: 100px;
}
does this refer to the device points, pixels, or physical pixels?
Also I use this line
<meta name="viewport" content="width=device-width,initial-scale=1.0">
so the device should not be allowed to scale the device up or down.