It started very innocent: Some consulting company apparently was tasked to create a prototype of the credit rating algorithm. Quite appropriately, I would say, they did so in Excel. As you can easily tweak the logic, show input, intermediate results and output. And all can be manipulated by the client who does not need to know a thing about programming to do so. Great.
From there it went downhill: Apparently someone up the hierarchy thought "Wow, that's 80% of what we need, let's just add a little UI and ship it"
They added a UI, but not as a VBA UI as you might hope. No, they did the whole UI in different worksheets. Storing any intermediate data ... also on worksheets. Long story short, it was a mess, and a slow one for that.
Oh, did I say this was a multi-lingual application?
Production rollout was on Jan 2nd, Dec 31st around 4pm I found a bug in the other language, on the one machine which had the this language configured. I believe this was the only time I ever saw a programmer literally run down the office to that machine to debug this issue.
Can attest to this. Some of the things I've seen excel spreadsheets contorted to do horrify me.
I once got spreadsheet dumped on me to debug because it wasn't working. A colleague used the spreadsheet to 'generate' interest rates that were then input into a mainframe. Dug into the VBA spaghetti mess, turns out this 15 year old script that took 15 minutes to run originally hit a bunch of Oracle/External APIs and performed calculations was now just copying the rates in from a csv file on a shared drive.
The error was caused by an excel formula ticking over a new year causing it to look for a directory it did not need to access that didn't exist. I thought it was pretty funny until I heard that the entire asset finance business had been unable to write any loans for days because of this.
