interval analysis

Essential reading

Incorrect use of Excel's NPV function is a common source of spreadsheet errors. We show several pitfalls and ways to avoid them.
Spreadsheet errors are reduced by using good design. Our students do three assignments to acquire good spreadsheet design skills.
95% of all spreadsheets contain errors. So, it is almost certain that your spreadsheets are wrong.
This article walks you through different methods and built-in tools that can be used to audit and debug Excel spreadsheets.
Research concludes unanimously that spreadsheet errors are both common and non-trivial. We must seek ways to reduce spreadsheet errors.
"Oh My God" my formulas are not working! This article covers most of the reasons for Excel formulas not working. And how to fix them.
Once information is loaded into a spreadsheet, it acquires properties that it may not deserve – a process called reification.
Our spreadsheet methodology has criteria for designing, building, and validating spreadsheets to ensure that they work correctly.