I'm usually not such a huge fan of people promoting websites or products in these forums, but I do think that this app is an interesting one and something useful to people who visit here. The thing that disappoints me is that it isn't a free app - or at least a lot less than $5. Also, looking at this listing on itunes
there is a review by a licensed optician which says that the measurements are not very accurate with this app - sometimes off by as much as 3mm. I'm not sure how much faith to put in that review, though, as the review also seems very negative towards ordering glasses online, which is the situation for which this app is most likely to be used.
Perhaps someone else can compare the accuracy of this app with real tools and also compare to the freely available methods people can do on their own.