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

Stopwatch and Timer Calibrations
5.C.4.c. Combination of Uncertainties
In the following examples, the uncertainty budgets were developed for a
calibration using traceable land lines (Table 8 and Table 9), and for a calibration
using a cellular phone or satellite signal (Table 10) based upon the data previously
provided. The human reaction time was based on the worst case data presented
in Section 5.C.2. The uncertainties are rounded to the nearest millisecond. The
uncertainty components are considered to be uncorrelated, so they are combined
using the root sum of squares method.
Table 8 - Uncertainty analysis for direct comparison method (digital DUT)
using a land line.
Source of
uncertainty
Human reaction
time bias
Human reaction
time standard
deviation
Telephone delay
deviation
Magnitude,
ms
Method of
evaluation
120 Type B
230 Type B
30 Type B
Distribution
Rectangular
Standard
uncertainty, ms
69
Normal
(k = 1) 230
Rectangular
17
½ DUT resolution 5 Type B
Rectangular
3
Combined uncertainty 241
Expanded uncertainty (k = 2, representing approximately a 95 %
level of confidence)
482
38