InControl will be happy to measure and mark the mounting locations for all of our airflow stations-- we do it for free and strongly encourage it. That way you know that you have the correct size and the best mounting location to make sure we get the full accuracy of the device.
There is some mounting flexibility in the brackets, depending on the installation type:
For internal brackets, aproximately +/- .75" by adjusting the set screw on the mounting feet. DON'T OVERTIGHTEN the screws on the feet, especially on the cable end.
For insertion mount, the probes are cut full size but there is a 1.5" stud on the non-cable end that allows for some adjustment. About 1", especially to make the probe fit a LARGER duct than measured.
For standoff mounts, the brackets need to go straight back to the damper frame, there isn't much flexibility on these. It would be best to get these right on or slightly larger than the damper opening.