We propose a fuzzy inference ruler using d'Ocaone's nomography. We will be able to get the results of fuzzy inference by the ruler without computer. As the inside of the black box of fuzzy inference will be visible on the ruler, it is expected that the fuzzy theory will be generally accepted and utilized by most persons. In this paper we will first refer to the nomogram, then describe how to apply the ruler to fuzzy inference, and we will discuss about the fuzzy inference ruler made as a trial for deciding exposure parameters of radiography.
