Seat tube angle listed incorrectly?

RickTChemist Posts: 90
edited February 2014 in Workshop
I'm confused....

I was just idly fading around with my training bike and decided to use my funky new app to measure the frame angles. I have a Planet X team Alu which has a STA listed at 72.5 degrees. Upon measuring the STA (on level ground) the app records 70 degrees. I have checked the app and it is accurate.

Why would the actual STA be much lower than advertised?