http://www.spotmarksthetax.com/ In order of increasing power consumption, Spot takes three kinds of location fixes: a Venue Fix, a Tracking Fix, and a Fingerprint Fix. Venue fixes have an entry time and a duration. For example, say you were visiting a client’s office for an hour long meeting. Spot would take a fix about 5-15 minutes into the meeting and a second fix roughly 5-15 minutes after you’ve left the office to declare a venue fix of your location, time and duration, perhaps for 67 minutes and 13 seconds. A Venue fix exploits Apple’s location database of both cell towers and Wi-Fi access points. While these are not as precise as GPS measurements, in practice, they are quite good. We believe that these fixes alone are sufficient to handle most tax residency issues. Consuming a bit more power are the optional Tracking fixes. These fixes are calculated when the phone switches cell phone towers. While they typically have an accuracy radius of about a kilometer, they are also, in practice, quite accurate in showing the progress of your day. Finally, a Fingerprint fix, which is taken by running the app and pressing the fingerprint icon in the upper left corner, uses the GPS to record your position with the highest resolution possible. When you need to prove that you have crossed that state line before midnight, the Fingerprint fix is what you want to use. Since its accuracy radius can be as large as 65 meters, more than half a football field long, make sure you are significantly past the state line when you take the fix.