Ansco X-Ray Exposure Guide (ca. 1950s)
This slide rule was manufactured by Ansco of Binghamton New York, and it probably dates from the 1950s. Prior to WWII, Ansco belonged to the German company GAF. During the war, the company was taken over by the U.S. government and operated by a trustee until 1965. This connection to the U.S. government probably explains the slide rule's colors: red white and blue.
It was used to help identify the suitable distance-high voltage (kVp) combinations for performing X-rays of extremities (e.g., wrist, feet). Tests were first performed to determine the high voltage that provided a good X-ray image of the wrist at 5 cm (2 inches). The slide rule was then set at this combination and the ends of the slide were cut off. Once this was done for a given X-ray unit, all the suitable distance-high voltage combinations could be read off the slide rule.
Size: 2.5" x 7" (cardboard)