Lešenie

A tool for a scaffolding rental: wall dimensions in, parts list, weight, number of trips and a priced document out. Ten mistakes turned up in the spreadsheet it replaced.

Where the problem was

A sole trader rents out scaffolding. He ran the whole business through one Excel. It held how many parts a given wall needs, how much it weighs, how many trips it will take, what is in stock and what he invoices it for.

He called saying he wanted “an app instead of Excel”. Most people would start programming at that point. I started reading the Excel.

What I found

I took the workbook apart cell by cell and rewrote it into clean formulas. And in doing so something turned up that the client had no idea about: there were ten mistakes in his calculation.

The most-used part in the whole set never entered the weight, invoice or stock calculation. It simply was not there. VAT was calculated, but never added to the final total.

That means he had for years been sending quotes that were quietly wrong. Not by a few cents, but by parts he charged for or did not, and by trips he planned badly.

It came to light because I asked before building. I wrote a list of thirty-eight questions and did not start designing the database until the answers came in. I never guess, because in a calculation like this guessing only shows up when someone sends a price to a customer off the back of it.

What I built

A small, finished thing. You enter the wall dimensions and out comes a parts list, a price and the decision on how many trips it will take based on the total weight. Plus stock, customers and a document ready to print.

It also includes a preview of what the built scaffolding will look like, so you can check it with your eyes before sending a quote anywhere.

The calculation tests compare the results directly with the original Excel. That was deliberate. The client had to see that the new app calculates the same thing he knows and trusts, except at those ten places where the Excel calculated wrong.

What it brought

Quotes that add up. And an answer to the question every client should ask before hiring anyone: how do you start?

Speed is a fine thing, but building the wrong thing fast is still building the wrong thing. Here the most valuable part of the work was done before the first line of code fell.

Under the hood

React and Supabase, deliberately without big libraries and without server functions. A tool for one person does not need a platform. It needs to work and to be understandable. Deployed on Netlify.

The calculation core is separated from the rest of the application, so it can be tested on its own. That is exactly what made it possible to compare it with the Excel line by line.