Ineffective at best

I (foolishly) assumed the app would use the photos focal length and determine measurements by triangulation. I was incorrect. Additionally, the app doesnt incorporate edge distortion (inherent to any fixed lens) so accuracy is lost exponentially as the measurement calipers approach the edge of your photo. A $3.99 app should be of a substantially higher caliber. Check the emailed receipt from iTunes to have your money refunded.

LousyHammer about RulerPhone - Photo Measuring, v4.52