So, it is winter, but I thought, "What the heck", and bought this. I was instantly impressed. The calculation was pretty much spot on to my existing polars. I don't update everytime I am out, but with this and the ability to set a percentage of efficiency, it is going to be in my top 5 best "friend" apps. The ability to export into Weather4D Pro and optimize routes is great! The fact that is an iOS app and is intuitive out of the box just adds to my fondness of it. Since everyone I sail with either has an iPhone or iPad or both, I just have to show them once how to use it and they can then tweak it without bothering me while I am off shift. I am also seeing how I can take this with me when racing with others and help to improve their boats. The only thing I wish I could do is print my chart. While it is super elegant on the iPad, sometimes you want a printout in a page protector that can be stuffed in a pocket. Yes, I could install on my iPhone, but paper sometimes is just better on a boat. Otherwise, this is great!