Instructions for Use
Divide the actual ball diameter or the length of the optical comparator by the measured apparent length of the comparator on the film. Multiply this answer by the pipe wall thickness as measured on the image media.
Actual Pipe Wall = (Actual Ball Diameter ÷ Ball Diameter on Film) x Wall Thickness on Film
For accurate measurement, the ball must be put as close as possible to the exact side of the pipe parallel to the image media so that the enlargement of the pipe wall is the same as that of the ball.
If the comparator or ball is not touching the pipe because of insulation, aim the source at the center of the space between the two. This will help ensure an equal amount of enlargement to the ball and the pipe wall. (Think of how the source side of an elliptical 2” weld is distorted more than the film side.)
For more information, see manufacturer’s product sheet: Exposure Reference Ball Cube – Product Sheet