<prompt> Compared to round PID, use of rectangular PID reduces the patients skin surface exposed by:15304560  <response>: There are several means to limit the size of the x-ray beam. First, a rectangular position-indicating device PID may be attached to the radiographic tube housing. Use of a rectangular PID having an exit opening of 3.5 cm × 4.4 cm 1.38 inches × 1.34 inches reduces the area of the patients skin surface exposed by 60 over that of a round 7 cm PID.White and Pharoahs Oral Radiology Principles and Interpretation 8th edition 