Part 2: So I used it out on the golf course. It was extremely easy to measure the distance of my shots. I kept my phone in my pocket, took it out to hit 'reset' after the shot, walked to the ball and looked at my phone - simple as that. I know that it was accurate to about +\- 5 yards based on the green indicator that said I had a good satellite signal. ( see part 1 below) I also tested it against the odometer in my Honda Accord for trip lengths of 1.00 3.00 and 5.00 miles. It was right on and I mean so close that I have no way of knowing which was more accurate. I'd bet the app was. I put my iPhone 5s on the dashboard to get the best signal. Part 1: So I was a scientist and know how to run experiments. I bought this app to measure the distance of my golf shots so I can better select clubs. It's hard to judge distance by eye and I'm a lousy golfer. I don't want to be messing with a laser rangefinder or a complicated/expensive golf mapping gps app. I've been tinkering with this app for a couple days and here's what I've found... It works very well subject to the limitations of the gps hardware/software in my cellphone. It can't make my iPhone GPS magically better, but it does a great job with what my iPhone and a sky full of GPS satellites give it to work with. Here's why I say that. I bought MegaTape and also bought another much more sophisticated diagnostic app (GPS Diagnostic) to get a detailed analysis of my iPhone 5s gps performance and satellite signal quality at locations where I'm standing or walking. I switched back and forth between the two apps while standing or walking to see if the MegaTape red/yellow/green indicator correlated well to the +\- accuracy value on the GPS Diagnostic app. Yes it did, very nicely. When the MegaTape app shows green for 'best GPS signal' the diagnostic app most always reads the best accuracy possible, a 17 foot radius. When Mega is yellow, Diagnostic shows about 33 feet accuracy. Red on Mega is for poor accuracy and the Diagnostic app typically showed accuracy at a hundred feet or more. Outside measurements are superior to inside where GPS signals lose strength. Both apps show that same result. So, MegaTape is doing the best it can with my iPhone hardware/software and the satellite signals my iPhone receives. Repeatability of results seems to be very good subject to the limitations I've mentioned. Therefore the accuracy and precision of this app are determined by the iphone, satellite positioning and obstructions, not the app itself. Not all phones with gps are created equal. The iPhone 5s GPS is supposed to be accurate to about 5 meters ~ 17' under ideal conditions and that's exactly what's revealed by both apps. I straight line walked my property about 20 times. Frontage is 155 feet (surveyed value). The MegaTape app with a green indicator is averaging 159 feet and is typically off by six to fifteen. My frontage has lots of trees and both apps show peaks and valleys in gps satellite signal quality. I spent a long time looking for an app like this one and couldn't find anything else that is as simple to use for the purpose of walking off distance measurements. Most all GPS apps are complicated to use, a lot more expensive and subject to exactly the same limitations of GPS on a cellphone. The laws of physics say they would not be any more accurate on my phone. Obviously, the 17 to 33 foot accuracy radius (green - yellow) isn't usable for distances below 50 yards, but for 50 - 250 yards and above it's great and the 5 meter accuracy limitation becomes increasingly less important with longer distances. It makes good sense to Google your phone to see what kind of GPS accuracy it's capable of before you commit to any GPS phone app.