Abstract: A meter for measuring the transmissivity of a floppy disk including an oscillator for generating a sinusoidal signal, a driver and an LED, biased on by the driver and modulated by the driver responsive to the sinusoidal signal, the LED for illuminating a portion of a surface of the disk. The meter further including a photodetector optically aligned with the LED and so disposed as to develop a detected signal from illumination transmitted through the disk, a current to voltage converter, an amplifier, a state variable band pass filter, and a peak detector and amplifier for amplifying, filtering and detecting the detected signal to develop a signal suitable for driving a digital panel meter so as to directly indicate in percent the transmissivity of the disk.