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Purpose: A new method of measuring visibility taking context into account introduced by Alexander Wertheim has been validated in this study. The purpose was to see if a simple and practical technique could render robust and useful quantitatively measurable results. Methods: An ordinary traffic sign, placed against different backgrounds, was used as a target. Subjects were told to fixate the sign and then slowly deviate with their gaze until they could no longer see the sign in the corner of their eye. This angle was then used as an index for conspicuity. A simple paper and pen method was tested as well as a computer based method. Results: Results for the paper and pen method showed low variance among subjects and a clear correlation between the conspicuity index and intuitive judgments of the visibility of the signs against different backgrounds. For the computer based method the variability was higher but the results still significant between the two groups of dynamic versus static signs. Conclusions: The conclusion is that the conspicuity index method is a simple and useful method that renders quantitative measurements of the visibility of targets taken context into account.