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RE: Spreadsheets (was "mathcad")

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I don't consider a spreadsheet adequately documented for final design
computations unless the spreadsheet results can be checked by an engineer
without having to open the spreadsheet or even knowing how a spreadsheet
works. Thus, I always type in a representative formula in the cell next to
the result, e.g.:

fb = P/A + M/S = 

Assumptions, constants, variables, etc, must be clearly defined, as they
should for any manual calculation. 

Such a spreadsheet can then be checked in one of three ways:

1. A simple mathematical check of results, using the formulas as presented
to manually check the results presented. This would be the same as checking
a manual calculation. This checking method works best for a spreadsheet
being used for a limited number of applications for a given project. 

2. A complete check of internal cell formulas within the spreadsheet. (In
this case the checker must be familiar with spreadsheet development.) Once
the spreadsheet is fully checked for an application, only the input and
applicability of results would need to be checked for multiple similar
applications. 

3. Thorough documentation, including checking of all cells, clarity of
presentation, limitations of spreadsheet and of results, etc. Non-input
cells should be locked to prevent changes and only the preparer should make
modifications to the cell formulas. This detailed checking and spreadsheet
development method can be used to develop a "master spreadsheet" which can
then be used for a variety of applications and projects. 


William C. Sherman, PE
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com

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