pixel per degree (ppd)
Pixel per degree (ppd) is a characteristic value for the image resolution of displays and VR glasses. This characteristic value depends on the viewing distance and thus on the field of view and the visual acuity of the viewer.
The magnitudes of ppd values are in the range of over 10 ppd and can be several hundred pixels per degree. This means that one degree of angle change on the display is represented by over 10 pixels. For VR glasses and VR headsets, the pixel-per-degree values are between 10 and 20.