Spreadsheet Day

What the day is

Spreadsheet Day is observed on October 17, marking the release of VisiCalc in 1979 for the Apple II.

Origin and background

VisiCalc was written by Dan Bricklin and Bob Frankston. Bricklin's account is that the idea came to him as a business student, watching a professor correct one figure on a blackboard ledger and then rework every dependent number by hand. He wanted a blackboard that recalculated itself.

The result is the concept every spreadsheet still uses: a grid of cells, formulas that reference other cells, and automatic recalculation when anything changes. That last part is what mattered. It turned a static table into a model you could ask questions of, and made the phrase what if a practical operation rather than an afternoon of arithmetic.

Its commercial effect was extraordinary. Businesses bought Apple II computers specifically to run it, and the term killer application was coined to describe exactly this: software so useful that people purchase hardware in order to use it. Lotus 1-2-3 later dominated the IBM PC era for the same reason, and Excel took over from there.

The consequences are still with us. Enormous quantities of the world's financial modeling, scientific data handling and operational planning run on spreadsheets, often built by people with no software engineering training and no version control. Spreadsheet errors have caused documented losses in the hundreds of millions and have affected published research and government policy, because a spreadsheet looks authoritative in a way a rough calculation does not.

How to take part

• Learn one function you have been avoiding. Lookup functions and pivot tables repay the hour many times over.
• Audit a spreadsheet you rely on. Check the ranges in the formulas at the edges, which is where errors hide.
• Separate inputs, calculations and outputs into distinct areas or sheets.
• Never hard-code a number inside a formula. Put it in a labeled cell and reference it.
• Keep dated copies of anything important. Spreadsheets rarely have any other version history.