This is a VERY easy to use device, it actually comes with no instructions. It has two functions: it measures the length of the path you walk/drive/ride, or it measures the AREA you walk/drive/ride. You need to set the time in UTC and then + or - for your location. Example: Houston, Texas is UTC-5. Now all log files have day/month/year and then the time. If it's wrong, it's nearly impossible to recover what you measured. I use this to measure the length of a driveway, the amount of water on the property, the length of the street, etc. I also use it to get the lot/parking lot/pasture area and even get the size of a store, building or backyard patio. For less than $100, I'm very impressed with what it does. It uses GPS and GLONASS for ultra-precise measurements. It's much easier to use this for estimating jobs like mowing, haymaking, fencing, etc.