Your object has a shape (square, rectangular, round, or some combination). The wizard will configure an optical system to let you fit the entire object onto the sensor (or make sure that a line scan camera is able to scan the longest dimension).

For a square or rectangular object, enter the side of the square, or longest side of the rectangle. The wizard will produce the magnification required to fit this dimension within the vertical dimension of the sensor or length of the line scan.

For a circular object, enter the diameter, and the wizard, again, will fit this dimension within the vertical sensor dimension or length of the line scan.

When you pick a standard camera format, the wizard knows the vertical dimension of the sensor. Otherwise, it will calculate based on the value entered for vertical or line scan under "other".