A sensor positioned on the opposite side detects the amount of light that passes through; the key is that the marks made by a pencil are graphite, which is opaque and absorbs light, while the empty bubbles allow light to pass through more readily. If the scanner detects that no bubble in a specific zone is filled, or if it finds two bubbles filled simultaneously, it flags the question for review.
The Mechanics of Optical Mark Recognition in Modern Education
Educational institutions use the data to analyze question difficulty, identify trends in student performance, and refine curricula. At its core, a scantron is an optical mark recognition (OMR) device designed to translate physical pencil marks into digital data.
The Fundamentals of Optical Mark Recognition The operation of a scantron relies on the principle of contrasting light absorption. One common method is the detection of "no marks" or multiple marks in a single bubble.
How Scantron Sensors Detect Marks Using Light Absorption
The software then compares the darkness of each bubble against a threshold value; if the darkness exceeds this threshold, indicating a sufficient concentration of graphite, the bubble is marked as filled. How the System Interprets Marks The system differentiates between a filled bubble and a blank one based on the amount of light that returns to the sensor.
More About How does a scantron work
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