Projector Screen Size Calculator

I've been suggested through the comments to create a calculator for image projection. Yesterday I was figuring out how to do it and it's really simple, but I want to ask you again.

What do you prefer?

1. A FREE APP with no database (you write 2 or 3 values from the datasheet of the projector) and get the result
2. A PAID APP with a database of the most popular projector (so you are limited to find the model you want in the database and requires upgrades)

THANKS AGAIN FOR YOUR GREAT FEEDBACK!!!