Here is something interesting I copied off a posting in bbc forum.

DISPLAY RESOLUTIONS


700 series 5” display 640 X 640 pixels = 31,170.5 pixels per square inch
800 series 7” display 480 X 800 pixels = 17,533.4 pixels per square inch
900 series 8” display 480 X 800 pixels = 12,755.7 pixels per square inch
1100 series 10.4” display 600 X 800 pixels = 8,858.2 pixels per square inch

ONIX-8 8.4” display 768 X 1024 pixels = 23,301.7 pixels per square inch
ONIX-10 10.4” display 768 X 1024 pixels = 14,513.2 pixels per square inch

Helix-5 5” display 480 X 800 pixels = 33,436.7 pixels per square inch
Helix-7 7” display 480 X 800 pixels = 17,294.9 pixels per square inch
Helix-9 9” display 480 X 800 pixels = 11,393.1 pixels per square inch
Helix-10 10.1” display 600 X 1024 pixels = 14,221.2 pixels per square inch
Helix-12 12.1” display 800 X 1280 pixels = 15,625.2 pixels per square inch

SOLIX-12 12.1” display 800 X 1280 pixels = 15,625.2 pixels per square inch
SOLIX-15 15.4” display 800 X 1280 pixels = 9,846.2 pixels per square inch