I notice the the algorithm you use to calculate the distance when using the measure tool rounds your distance, but it doesn't appear to be rounding it properly every time (or calculating it correctly for that matter). For example click and drag it to the right until it says about 70 feet. Cool, now while still measuring move it along the y axis 15 or so spaces. So you now created a 14x15x20 triangle where your horizontal move was the 14, the vertical move was the 15, and the measure is the hypotenuse which is 20 units long. Now if each unit represents 5 feet in game, the measuring tool should report a measurement of 100 feet, but instead it says 75 feet.