spreadsheet engineering analyses the good the bad and the ugly
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Spreadsheet Engineering Analyses : The Good, The Bad, and The Ugly. D Raj Raman January 23 rd , 2013. Why Use Spreadsheets?. Readability neater than all but the most fastidious engineer with his or her mechanical pencil Readily modified Can look at “what if?” scenarios Can easily debug

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Presentation Transcript
why use spreadsheets
Why Use Spreadsheets?
  • Readability
    • neater than all but the most fastidious engineer with his or her mechanical pencil
  • Readily modified
    • Can look at “what if?” scenarios
    • Can easily debug
      • E.g., error in an assumed value
why use spreadsheets1
Why Use Spreadsheets?
  • Easily presented visually – fairly powerful graphing capabilities
  • Higher level analyses possible
    • Visual Basic for Applications (VBA)
    • Built in tools (e.g., solver)
    • Many add-ons available
an overarching question how much detail
An Overarching Question: How Much Detail?
  • Conciseness is a virtue
  • Excessive brevity (to the point that others cannot follow your work) is a fault!
    • Both these statements also apply to written engineering solutions!
good spreadsheet practice 1
Good Spreadsheet Practice #1
  • The only numerical values you should enter are givens or assumptions
    • These should be clearly listed together on a common area or tab of the workbook
    • They should be given with units (or explicitly listed as dimensionless)
    • All other values should be calculated
      • And calculations should be done so that intermediate steps are clearly visible (with units) for crosschecking
good spreadsheet practice 2
Good Spreadsheet Practice #2
  • When possible, keep contents visible on a single desktop (or page)
    • Use multiple tabs to handle larger projects (like ours)
    • Realize that for some data intensive problems, this won’t work
      • Use “Freeze Panes” under “Window” menu to ensure that headings and row titles are maintained on large sheets
good spreadsheet practice 3
Good Spreadsheet Practice #3
  • Make the sheet itself visually informative
    • Color
    • Fonts
    • Conditional Formatting
    • Present only a reasonable number of significant digits
      • Select units carefully and convert appropriately
      • Use scientific notation
good spreadsheet practice 4
Good Spreadsheet Practice #4
  • Be absolutely confident in your use of relative and conditional addressing
    • Screwing this up leads to major errors!
good spreadsheet practice 5
Good Spreadsheet Practice #5
  • If there are values (e.g., physical constants, conversion factors) that recur in many equations on your sheet, name them rather than using absolute addressing
    • Much easier to read and debug cell equations if you do this
good spreadsheet practice 6
Good Spreadsheet Practice #6
  • Make your graphs consistent
    • Make your first graph and spend time getting the formatting correct
      • graph should be separate sheet of the workbook
    • Copy the formatted graph repeatedly
    • Change the cell references in the graph sheet
bad spreadsheet practices
Bad Spreadsheet Practices
  • Insufficient detail
  • Computed values entered by hand, based on calculator
  • Intermediate calculations not shown
    • Excessively long equations
  • Constants not given names
  • Conversion factors not listed explicitly
  • Assumptions listed multiple times
    • No “one stop” changing of assumptions
ugly spreadsheet practices
Ugly Spreadsheet Practices
  • Givens, assumptions, intermediate, and final computed values intermixed
  • Flow unclear
  • Lack of spatial organization
  • Poor font selections and no use of font or color to delineate information
  • Excessive significant figures
  • Row and column headings not “frozen” for large sheets
  • On graphs, variations in font size, font selection, line width, etc. look amateurish
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