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

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.
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