Radiation exposure gauge

A gauge for use with x-ray machines to distinguish the following five x-ray film conditions, overexposure, upper limit of correct exposure, correct exposure, lower limit of correct exposure, and underexposure, by examining film densities at the upper and lower limits of the visible density range, consisting only of:

• a. first means for achieving a film density at the low end of the visible density range in a first film region;
• b. second means for achieving a film density at the high end of the visible density range in a second film region;
• c. third means for achieving a film density, in a third film region, slightly higher than the low end of the visible density range, said third region being contiguous with the first film region;
• d. fourth means for achieving a film density, in a fourth film region, slightly lower than the high end of the visible density range, said fourth region being contiguous with the second film region,
• such that the degree of visibility of the difference between the film densities in said first and third regions and the degree of visibility of the difference between the film densities in said second and fourth regions indicates the correctness of the exposure of the x-ray film.