Not accurate distance

Love the app as far as the icons showing what it where. Not very accurate with the distances though. I dont feel this was always the case. Its like somewhere along the lines it got switched to air miles or something. I have an example, I am at exit 200 off I10 in AZ, to exit 139 app says it is 52 miles away but basic math it is actually 61 miles away. If you increase the distance then the miles away increases.

Big Truck Chuck about Truck Stops Pro, v3.0.5