Part 1: I'm a financial model builder since Excel came out on the MAC in 1987 (I’m now however a PC and 63 years old www.fser.net). Some of the inaccuracies are caught using accounting articulation points: Assets = Liabilities + Shareholders' Equity... if out of balance, something is wrong... What is wrong is a bit tricky and takes thorough understanding of how Income Statements, Balance Sheets and Cash Flow Statements interact. Unfortunately, articulation points don't catch algorithmic mistakes. My models have some very complex algorithms built over the years and the best thing to do is graph each line “quickly”, looking for breaks or unusual patterns in each line item. My models are regularly 3,000 to 5,000 lines long - not because I like complexity, but because I have lots of ways of expressing revenues and expenses. I can model most business in a few hours. Recently, I built a steady state feasibility model for growing, harvesting and extracting lipids from algae using heterotrophic and autotrophic systems. I did make a graphing tool that would allow me to capture the relationship between any input and output as I incremented an input 10 times. In most cases the output was basically linear as the model was basically a linear calculator… I would suggest any builder of engineering models to implement an incrimination graphical recording system as an error checker.