Your spreadsheet as a city

The lots

Every non-empty cell, laid out where it sits on the sheet. Assumptions down the left, one quote per row, totals along the bottom. Pale lots are numbers somebody typed. Blue lots are formulas.

The skyline

Now let each formula rise by how much depends on it from upstream. The quote totals are tall. The grand total at the far corner is the tower, resting on nearly every cell in the book.

That is the thing about a spreadsheet. The number everyone reads is the one with the most underneath it.

One formula

Up in the assumptions, the loaded labour rate should be the wage plus 32% for taxes and benefits: =B2*(1+B3). Someone typed =B2+B3. It adds 0.32 dollars instead of 32 percent.

It looks fine. It is a plausible number. Nothing turns red in a spreadsheet. Keep scrolling and watch where it goes.

The lean

Every labour cost reads that rate. Every price reads the labour cost. Every total reads the prices. One cell, and of the formulas in the book are now wrong, including the tower.

The quotes went out under where they should have been. Nobody would know until the job lost money.

Why this keeps happening

Not because people are careless. In a spreadsheet a rate, a formula and a typed number all look the same, live in the same grid, and can be overwritten by anyone with the file open. The structure that would catch the mistake is not there.

In a proper system the labour rate is stored once, as a rate, and every quote reads that one record. There is no copy to drift and no formula to mistype on row nine.