Monday, January 30, 2006
Crossfooting
Over the weekend I had the task of building a spreadsheet model of several hundred numbers and math functions for a potential PR client. It wasn't complicated, just tedious. But, there is a truism about such models that is worth reminding practitioners about, especially those who don't build models often.
Always crossfoot numbers.
For those who don't do such things, crossfooting numbers calculates them in two directions where possible -- down and across. It's a maddening fact that spreadsheets with user-friendly functions can insert formulae in strange ways when one isn't looking closely enough. It happened at least twice on Saturday, and errors did not show until crossfooted totals did not match. That meant plowing through three worksheets to find where the SUM function had added a row when I wasn't looking and had failed to complete a row when I was.
The nice part of models is that one can play with them. In this case, it is important because it looks at a 3-year time expenditure of a CEO in several communications duties. The CEO can vary monthly hours up and down to get an idea of how much communications tasks will impact everything else he does.
Always crossfoot numbers.
For those who don't do such things, crossfooting numbers calculates them in two directions where possible -- down and across. It's a maddening fact that spreadsheets with user-friendly functions can insert formulae in strange ways when one isn't looking closely enough. It happened at least twice on Saturday, and errors did not show until crossfooted totals did not match. That meant plowing through three worksheets to find where the SUM function had added a row when I wasn't looking and had failed to complete a row when I was.
The nice part of models is that one can play with them. In this case, it is important because it looks at a 3-year time expenditure of a CEO in several communications duties. The CEO can vary monthly hours up and down to get an idea of how much communications tasks will impact everything else he does.
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