A novel D-serine quantification method that can overcome various disadvantages of a conventional D-serine quantification method; a novel enzyme that can be used in the D-serine quantification method; a gene encoding the enzyme; and the like. The down counter also includes a control line configured to alter the terminal count detected by the detection circuit by an off-set. The instant device includes a combination of two or more dielectric materials and provides impedance matching at the input and output ends as well as impedance conservation during propagation of the optical signal through the device. An exhaust vents heated air from the housing. The detection is performed by acquiring the image of the reticle under the same optical conditions as the exposure conditions, and by comparing multiple dies to find errors in the line width.