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Stopwatch and Timer Calibrations Figure 15. Measured reaction times (four operators, 10 runs each) for totalize method. As shown in Figure 15, the average reaction time was usually less than 40 ms. The largest deviation was about 90 ms. The mean and standard deviations for each operator were computed and graphed in Figure 16. The data demonstrates that the worst case mean reaction time was 27 ms, and the worst case standard deviation was 10 ms, which is a significant improvement over the direct comparison method. Subsequent measurements of human reaction time were made by placing the start/stop button of the stopwatch directly against the start/ stop button of the frequency counter (as shown in Figure 12) so that both buttons were pushed at the same time. The experimental data showed that this method provided no significant advantage over using one hand to start the stopwatch and the other hand to start the frequency counter. 44
The Totalize Method Figure 16. Mean reaction times (four operators, 10 runs each) for the totalize method. 6.B.3. Uncertainty Due to the Counter For this method, the uncertainty of the counter is related to the counter resolution. The internal time base of the counter is not used, because the gate time is controlled by the manual start/stop function. This method does not use the counter gate or trigger, so the uncertainties associated with these functions are also eliminated. The counter is simply used as an event counting device, and the uncertainty is equivalent to ±1 least significant digit on the display. 6.B.4 Device Under Test (DUT) Resolution Uncertainty Since the totalize method involves observing data from the DUT, the resolution of the DUT must also be considered. For digital indicating devices, resolution uncertainty is understood to be half of the least significant digit, with a rectangular 45
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NIST Recommended Practice Guide Sto
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Certain equipment, instruments or m
Page 7: Acknowledgements ACKNOWLEDGEMENTS
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Page 15 and 16: Section 1 Introduction to Stopwatch
Page 17 and 18: Introduction s or 42.13 s, but tha
Page 19 and 20: Introduction basic principles that
Page 21 and 22: Introduction and their traceabilit
Page 23 and 24: Description of Timing Devices Sect
Page 25 and 26: Description of Timing Devices Figu
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Page 29: Description of Timing Devices One
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Page 41 and 42: The Direct Comparison Method Secti
Page 43 and 44: The Direct Comparison Method Pleas
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Page 49 and 50: The Direct Comparison Method path,
Page 51 and 52: The Direct Comparison Method When
Page 53: The Direct Comparison Method Table
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Page 65 and 66: The Time Base Method Section 7 The
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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
Page 73 and 74: Other Topics Related to Measurement
Page 75 and 76: Other Topics Related to Measurement
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