Patent ID: 8538311

Claim:
A sheet measuring apparatus comprising: a first rotating member that includes a first peripheral surface portion that contacts a transported sheet, the first rotating member rotating as the sheet is transported; a second rotating member that includes a second peripheral surface portion, the second peripheral surface portion contacting the first peripheral surface portion and being made of a material different from a material of the first peripheral surface portion, the second rotating member rotating as the first rotating member rotates; a first rotation amount detecting unit that detects a first rotation amount that is a rotation amount of the first rotating member; a second rotation amount detecting unit that detects a second rotation amount that is a rotation amount of the second rotating member; a sheet calculation unit that obtains a first rotating member correction value for correcting an error that is superposed on the second rotation amount due to a radius distribution of the first rotating member in a circumferential direction and that performs calculation related to the transported sheet by using the second rotation amount and the first rotation member correction value; a radius distribution calculating unit that calculates a new radius distribution of the first rotating member in the circumferential direction by using the first rotation amount and the second rotation amount; and an updating unit that updates the first rotating member correction value to a new first rotating member correction value that is obtained on the basis of the new radius distribution.