Well....

Assuming a 16:9 60" screen, that would be 52.3 x 29.41...

52.3 / 1366 == .038 or 26.1 pixels per inch
29.4 / 768 == .038 or 26.1 pixels per inch

The 'diagonal pixel' thing was me being stupid - the pixels are square but the 16:9 diagonal is not a 45 degree line - the screen diagonal won't cross at the pixel corners. To compute pixel diagonal multiply by 1.4 (for square pixels)


Charlie