Nieco rzadziej "step wedge comparison film".

Densitometer and Step Wedge Comparison Film

7.2.1 Densitometers shall be calibrated at least every 90 days during use as follows:
a) A national standard step tablet or a step wedge calibration film, traceable to a national standard step tablet and having at least 5 steps with neutral densities from at least 1.0 through 4.0, shall be used. The step wedge calibration film shall have been verified within the last year by comparison with a national standard step tablet unless, prior to first use, it was maintained in the original light-tight and waterproof sealed package as supplied by the manufacturer. Step wedge calibration films may be used without verification for one year upon opening, provided it is within the manufacturer’s stated shelf life.
http://www.proz.com/kudoz/3347074

Tu więcej: http://tinyurl.com/2wcdcpo , http://tinyurl.com/36o98qc

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Note added at 1 hr (2010-06-04 20:30:30 GMT)
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Wygląda na to, że w kontekście chodzi o film porównawczy - trzeba będzie zdecydować, czy należy tłumaczyć dosłownie, czy interpretować. Oto definicje:

Step-wedge calibration film – A step-wedge comparison film the densities of which are traceable to a nationally recognized standards body.
Step wedge comparison film – A radiograph with discrete density steps that have been verified by comparison with a calibrated step wedge film.
http://tinyurl.com/25yckwg