As I mentioned, this app has got me off a mountain (and if I’m honest, I use it a little too much). Its simplicity is what makes it so good. All the mapping apps here will show a map grid reference to check against your paper map, and should work offline as long as there’s a GPS signal. GridPoint GB does this on a very simple page, and also demonstrates where you are within that square. It can always be worked out of course, but if tired and frustrated it’s an immediate reference. It also estimates the accuracy of the reading. Apps work best when they do one thing and do it well.