where r is the random variable (in this case, the uniform probability distribution) and [omega] is the width of the class interval about the quantised variable x in the step wedge
. This operation produces a random scatter plot suitable for regression analysis.
Concerning the radiopacity of materials, the International Organization for Standardization has stated that radiopacity is evaluated using the aluminum step wedge
technique with a range of 0.5-5.0 mm thickness at 0.5 mm increments at an accuracy of >98% purity and 0.05 mm variation in thickness .
Optical density means were calculated based on the measurements taken in three different areas of each sample and on the fifth step of the step wedge
(which corresponded to 5 mm).
The films were exposed to an optical step wedge
created by a software program built into the Kodak Dry View 8300 unit (Kodak, Rochester, New York).
X-ray machines are also submitted by their manufacturers to be certified as meeting certain standards - most notably the ASTM Step Wedge