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Listen to this post if you prefer
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- Something is extraneous in your formula
- you multiply an annual value by 12 by accident
- you capture 13 months in an annual sum instead of just 12
- Something is missing from your formula
- you forget to divide by 12 to convert an annual value to monthly
- There is an incorrect cell reference in your formula
- you forget to anchor one or more cell coordinates before copying and pasting the formula
- There is a misunderstanding of the business dynamic
- these are very hard to catch by yourself, as you don’t know what you don’t know
- Conditional logic is correct, but it is being triggered (or not) in a faulty manner
- you forget to round a referenced value, and the logic test in the formula fails to find a match as a result
- There is a unique Time 0 formula that has been applied to the operation period cells
- There is an external file link that produces an erroneous value
- There is a vestigial hard-keyed value from a prior use of the model that is no longer relevant
- Excel doesn’t warn you of its bugs
- when running a data table, you reference the model input in the header of the table (this is a wicked one, see here for more).
