I have one of those, and it has a series of patches centered on 18%. (So nominally the card is 18%). But I believe the way you use it attempts to "place" the exposure on 18%. You meter with incident light and shoot the card with a camera. Then you analyze the results.
You'll be pleased to know that the incident light reading does NOT agree with a spotmeter reading off 18%. It agrees more closely with a spotmetering off the 12.7% patch!

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