I believe Notch Size is the value the user inputs when they call up the app. I believe it SHOULD be the diameter of the bit but you can change it so it is bigger or smaller (I don't know why you would want to but you can).
Perhaps the best method would be to replace Notch Size with Bit Diameter, make it no longer user editable (or the user can select between their roughing bit or detail bit sizes), and change it to
var notchOffset = (params["Bit Diameter"]/Math.sqrt(2)) - (params["Bit Diameter"]/2);
@paulkaplan - Any input?