Snorkel Features. Material Details : The snorkel body is made of PVC tube, and the mouthpiece is made of food - grade silicone. Round the result to an integer multiple of 50 or 100. For example, if the astigmatism is 200 diopters and the myopia in both eyes is 350 diopters, then the selected power is 200/2 + 350 - 50 = 400 diopters.
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