Spreadsheets constitute a severe software risk for many companies and institutions. The impact of existing design, testing, and debugging tools on spreadsheet quality is limited, since spreadsheets often change owners and have to be used by people who haven’t created the spreadsheet. This flux often contributes to a lack of understanding, which is a major reason for mistakes in the use and maintenance of spreadsheets.

Based on the concept of explanation sheets, we present an approach to make spreadsheets easier to understand and thus easier to use and maintain. Explanation sheets are an instance of the idea of explanation languages. We identify the notion of explanation soundness and show that explanation sheets which conform to simple rules of formula coverage provide sound explanations. We also present a practical evaluation of explanation sheets based on samples drawn from widely used spreadsheet corpora and based on a user study.

In addition to supporting spreadsheet understanding and maintenance, our work on explanation sheets has also uncovered several general principles of explanation languages that can help guide the design of explanations for other programming and domain-specific languages.