I went to a meeting just before I retired. They were doing a presentation on the monthly budgets with all their clever clog spreadsheets. I could see an error in one of the rows ( as a wind up I got a slide rule out of my case ) the figure in that cell is wrong , I had done the sum in my head. They didn't know what a sliderule was, so it got them a bit frightened. Lots of fun that was.🤣