Here is the way I calculated it ....

Helix 10:
8.75" horizontal x 4.9375" vertical = 43.203 square inches.
1024 pixels x 600 pixels = 614,400 total pixels.
614,400 pixels divided by 43.203 Sq inches = 14,221 pixels per sq inch for the Helix 10.

Helix 9 :
7.75" Horizontal x 4.25" vertical = 32.9375 Sq. inches.
800 pixels x 480 pixels = 384,000 total pixels.....So the Helix 10 would have 230,400 more pixels than the Helix 9.
384,000 total pixels divided by 32.9375 Sq. inches = 11,685 pixels per sq inch for the Helix 9.

So, 14,221 - 11,685 = 2,536 pixels per sq inch difference between the Helix 9 and the Helix 10.

I rounded the 2,536 up to 3000 as a rough number......I have no idea what that ppi designation means.

With a combination of the larger square inches and the higher pixel density, the Helix 10 screen clarity will be a lot better than the Helix 9. This theory has been verified by people who have used both.