# Overview

Formula Forge, by Stage One Software, seeks to reduce the tremendous costs incurred by spreadsheet errors, which are all too prevalent in business.

## Sources of Spreadsheet Errors

There are many sources for errors, including poor development practices, formulas improperly copied from one cell to another, and errors in the text of a formula. Generally speaking, these errors can be categorized as practice errors, structural errors, and computational errors. Formula Forge is designed to reduce errors in the third category.

### Practice Errors

Practice errors result from failing to implement and/or adequately follow best practices such as how to handle constants. Best practice dictates putting constants in cells where they can be readily identified and referenced. Then, if a constant must be changed, only one cell has to be edited, not the many cells that contain the constant as a literal. Organizations that want to reduce or eliminate practice errors often utilize the services of training companies that provide best practices education.

### Structural Errors

Structural errors involve relationships among cells in a spreadsheet. A typical error occurs after a formula is replicated by copying it into a range of rows and/or columns. The copies of the formula are structurally the same, differing only in the relative references they contain. An error can occur, however, if one cell in the range is changed in a way that breaks the relationship.

Many structural errors can be found by spreadsheet auditing software. Such software can take the form of a plug-in or standalone program that reads and analyzes a spreadsheet to produce a report of structural inconsistencies as well as specific practice errors.

### Computational Errors

Computational errors arise from several common kinds of mistakes in formulas.

#### Parenthesis Errors

A formula's value depends on the order in which Excel evaluates its operations. Parentheses control this order, but the arrangement and grouping of these slim slim characters can be hard to see. Problems arise particularly when a formula contains many parentheses, which make it difficult to ascertain the evaluation order by simple visual examination. Other problems can while editing a formula: Excel may refuse to save the formula because its parentheses are not balanced, or it may save a faulty formula if its parentheses have been inserted incorrectly. Although Excel often suggests how to fix parenthesis errors, it can be hard to see if its suggestions are appropriate or what the correction should be.

#### Evaluation Errors

Evaluation errors cause formulas to produce the wrong result. For example, Excel evaluates `-X1^2` by computing `-X1` first and then squaring the result, contrary to ordinary mathematical and programming language conventions, which square X1 first.

#### Logic Errors

Complicated formulas often use branching functions, such as `IF` and `CHOOSE`. An error can occur if such a function chooses the wrong branch for conditional evaluation. The likelihood of such an error increases when these functions are nested.

#### Subexpression Errors

A complicated formula often often contains many subexpressions, which in turn may contain still other subexpressions. If the entire formula has the wrong value, the problem may be caused by an incorrect subexpression. Finding that subexpression can be very difficult. Pernicious and hard-to-find latent error often occur in unused branches of a conditional function.

#### Cloning Errors

Sometimes a formula contains the same subexpression multiple times. If the subexpression isn't copied exactly, it can introduce an error. Subtle changes in how characters are arranged can be difficult to see, and repetitive expressions in Excel's character-based formula bar make a formula difficult to read.

## Formula Forge: Stage One Software's Remedy

To date, there has been only limited help for finding and fixing computational errors, mainly on Excel's Formulas ribbon and in its help files. Stage One Software remedies this defect by offering Formula Forge, the first tool specifically designed to eliminate computational errors. Formula Forge integrates directly into Excel to provide multiple views of formulas that clarify their meaning and their evaluation.

• Its text view shows a formula's text as it appears in Excel's formula bar.
• Its math view shows a formula as it would be typeset in a book on mathematics, making it much easier to read.
• Its tree view contains a hierarchical diagram like an organization chart, showing how Excel decomposes a formula into its constituent elements, along with values for all its elements.

Users can highlight an element they wish to examine in any view. Formula Forge automatically highlights that element in the other views, enabling users to see where they are. Users can also collapse elements (to hide irrelevant detail and focus their attention elsewhere) and then re-expand these elements to examine them more closely.

A forthcoming release of Formula Forge will provide a drag-and-drop editor. With it, users can construct, debug and modify formulas easily and accurately using simple building blocks, without ever again having to worry about parentheses.