Thanks, I will give that a shot. I am trying out the method of measuring frequency using the Gates app to properly tension both sides.
Following this: Measuring belt tension, squaring and calibration
I notice the Shapeoko Pro has 15mm belts. Is there any chance you could do me a favor and provide the linear density of the new 15mm belts, in kg / m / cm? My understanding is this is calculated by dividing the weight of the belt by its surface area (i.e. weight / (15cm x length)) I am building a spreadsheet and just want to ensure I have the right value. That way in the future, others can reference this spreadsheet in setting the tension of their Shapeoko Pro properly 
Thanks in advance!