A reference cylinder is a true cylinder which is fitted to the analysed data in order to measure the deviations from it. There are four internationally recognised reference cylinders. These are the Least Squares, Minimum Zone, Maximum Inscribed and Minimum Circumscribed cylinders.
Least Squares
The least squares cylinder is constructed from the average radial departure of all the measured data from the least squares axis.
Minimum Zone
The minimum zone cylinder can be described as the total separation of 2 concentric cylinders which totally enclose the data and are kept to a minimum separation.
Minimum Circumscribed
The minimum circumscribed cylinder is a cylinder of minimum radius that totally encloses the data.
Maximum Inscribed
The maximum inscribed cylinder is the largest cylinder that is enclosed by the data