Great app
Response from developer
Hi, thanks for being a long time customer. BTW, we are coming up on our 12th birthday thanks to folks like you. The short answer is no you don't have to pay for existing functionality. When you purchased the app, the compare function was triggered by an icon the looked like a scale or balance. Now the compare function is accessed by a more legible icon. It is found at the bottom left of the gel view screen. The in app purchase is to view gels or photos through the camera much as you would look through a swatch from your gel book. Roughly 1/3 of our customers have added that functionality .