Stopwatch and Timer Calibrations - National Institute of Standards ...

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Stopwatch and Timer Calibrations Figure 18. Photo totalize stop reading. WARNING NOTE - In order for this method to provide accurate results, the photo system must be set up in a manner that captures the stopwatch and counter display correctly. If the shutter speed is too slow, the images will not produce discernable information, as Figure 19 shows for the stopwatch. We could interpret this stopwatch reading with the 1/10 s digit as 9, 7, 3, or 4, and the 1/100 s digit as 3, 5, or 6. Additionally, often when the photo yields a very clear display as in Figures 17 and 18, the resulting measurement is not valid. This stopwatch was previously calibrated using other methods described in this book and was found to have an offset of less than 1 second per day, which is significantly different from the photo totalize method results indicated above. For this example and photo equipment setup, the method produced false results. Anyone using the photo totalize method must validate the measurement results of their measurement process by comparing results obtained for a particular instrument to other measurement methods discussed in this book. 48
The Totalize Method Figure 19. Ambiguous photo totalize reading. Section 6.C.1. Advantages of the Photo Totalize Method Using this measurement method, all uncertainty due to human reaction time is reduced to zero. This makes the estimate of measurement uncertainty smaller, and the amount of time needed to complete a calibration shorter than the direct comparison or totalize method. This method also makes it possible to calibrate multiple stopwatches at the same time, and then maintain the photos as archival data. Section 6.C.2. Disadvantages of the Photo Totalize Method This method can VERY EASILY produce erroneous results. As previously stated, the measurement results for the particular cameras used by the laboratory should always be compared to measurement results of the same unit under test using other methods described in this book. 49
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NIST Recommended Practice Guide Sto
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Certain equipment, instruments or m
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Acknowledgements ACKNOWLEDGEMENTS
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Page 15 and 16: Section 1 Introduction to Stopwatch
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Page 19 and 20: Introduction basic principles that
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Page 23 and 24: Description of Timing Devices Sect
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Page 69 and 70: The Time Base Method 7.B.2. Using
Page 71 and 72: Required Uncertainty Section 8 How
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