A different approach to measurement uncertainties recommended by the
International Organization for Standardization in their publication
Guide to the Expression of Uncertainty in Measurement (GUM). and
suitable for use in introductory level physics courses is described
in The Physics Teacher vol 46 December 2008 page 539.
I
t can be downloaded FREE from the URL
<http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PHTEAH000046000009000539000001&idtype=cvips>