There are situations where several criteria are required to add up the right numbers. That's straightforward if the numbers are found in a single column using SUMIF. Yet when you find your data in several columns, more complex formulas are needed.

This article shows you how to use SUMPRODUCT with multiple criteria to add numbers from multiple columns.

A list of the top 10 worst nightmares for a financial modeller, and how to solve them:

• Cleaning up someone else's models.
• Circular references appearing where you did not expect them.
• The financial model crashes, and you don't have a backup.
• Worksheet compatibility issues.
• A balance sheet that does not balance.
• Changes in accounting standards or applicable fiscal regimes which, in turn, make your life miserable.
• The first time you are asked to build a cash-flow waterfall when the only waterfall you knew was Niagara Falls.
• Clients who have Excel phobia.
• When you are given a financial model in Portuguese and your level of Portuguese is limited to the lyrics of Amar Pelos Dois from Salvador Sobral.
• Being called a data cruncher.

This article explores a pitfall of using Excel's AutoSum feature.

When not used according to Excel's arcane set of rules, everything may appear okay but you can easily introduce an error where some values are omitted from the AutoSum.

A workaround is also suggested, to ensure that AutoSum continues working as expected.

Calculating a running balance is a common and important spreadsheet task.

But inserting rows, deleting rows, and moving rows via cut and paste can introduce hard-to-detect errors in a running balance formula.

This article explains the problems with the basic running balance formula and provides two robust solutions.

AVERAGE is one of those easy functions in Excel. Like, super easy! It has just one argument, the cells, or numbers to be averaged.

So what's the problem? It's too easy to get wrong, yet we might not notice for weeks, months, years or ever.

There are many ways to calculate an average. Different formulas will fit with different datasets and scenarios. The critical thing is to know your data and exactly what you want to achieve.

For more than 30 years, Excel's data types have been very basic: text, numbers, Booleans, and dates. The user had to assign meaning to the data, which often leads to errors.

But that is starting to change. Microsoft has introduced the concept of linked data types into Excel. The first two linked data types are Geography and Stocks.

This article describes the new data types, with examples of how to use them.

The new data types are being rolled out to Office 365 users this month.

Also see Excel help: Stock quotes and geographic data.

Have you seen the articles that blame Excel for all kinds of business errors?

In some cases, problems occur because rows were hidden, and that distorted the data analysis.

To help avoid those problems, I created a sample file that shows an Excel hidden data warning, if rows or columns are hidden.

Remember, as the old saying goes, it's better to be safe, than to read about your catastrophic errors on the internet.

This article provides example scenarios and explains various approaches for calculating the time value of money using Microsoft Excel.

The functions discussed include FV, FVSCHEDULE, PV, NPV, PMT, RATE, and NPER.

For more information, also see Pitfalls of Excel's NPV function.