Taking radiographs where the area of interest is not close to the plate creates some challenges in scaling. This is true of both digital and analogue systems. When using the radiograph for templating implants e.g. total hip replacement it is very important to make accurate measurements.
The Reference ball is 25mm in diameter and is attached to a stable base by a flexible neck which allows the ball to be placed at the same level above the plate as the area of interest. Using a spherical object as a refer-
ence eliminates errors created by ruler type reference which might not be quite parallel with the plate
Radiographic Reference Ball 25mm diameter.