Answer: The 2.75” inclinometer casing will be able to be read longer than the 1.5” PVC due to its larger diameter – the same way that 3.34” casing will be able to be read longer than the 2.75” casing. The larger diameter means that it will allow for more shear before it closes off completely.
The second advantage of casing over PVC is the ability to run traversing probes and spiral probes in the casing prior to installation of your permanent system. This is especially helpful in determining if you have an acceptable installation (angle from vertical, spiral, twist, etc.) prior to installing your permanent system. It is also helpful to be able to check the inclinometer in case there is ever a question about the results from your permanent system. While this is not often required, if it is needed the permanent system can be removed and a traversing probe run down the hole to validate the data. The traversing probe is not compatible with the PVC due to the lack of grooves.