Why replicate the same calculation with the same errors? Shouldn't it be specified as a pure math formula somewhere, probably in the contacts? So they did it slightly wrong for a long time, but why would that be the reference instead of the contract.
It hurts even when there is no explicit contract. After integrating a couple of factories we found out that not precision is king, but stability is. Too many processes depend on each other, from small to big, and if you’re lucky to mess it up without immediate notice from workers (which happens rarely, since they give a good friction on this slippery surface), costs to fix it may outprice the precision gains for years. Essentially, no matter what the hw/sw platform is, business “ABI” is locked into algorithms used, and rounding/floating/fixed is only one of these. I’ve seen [edit:algorithm-wise] wrong cost-price distributions, penalty calculations and so on, that were a foundation for chains of table-based and gut-based decision making. Things simply don’t add up for everyone, not to mention how hard is turning a switch for the entire org that runs e.g. 24/7 and/or has unfinished production shifts.
That was a knowledge I wish I already had back then, since these sorts of projects provided a lot of frustration, insecurities and expenses that you never could imagine working as software half-pm/half-coder. At some point you start to doubt whether you’re skilled for this job or just a loser with a keyboard.
Minor/simple processes lack that cohesion and can be fixed or left as-is without much trouble though.
The requirements doc or contract generated to create the software almost always has a lot less thought and a lot less debugging and adjusting in it than the actual software and processes subsequently built around it that have been running that way for the last decade oe three.
Can you imagine if, suddenly, an insurer had a 1% shift in premiums overnight because someone fixed the rounding algorithm to comply with the 1983 spec that had been mis-implemented in COBOL?
They weren't trying to replace the system, just emulate it for testing and simulation purposes: e.g. test how new rates would affect existing policy holders.
Insurance policies (the contracts) just have final premiums (sometimes they might split it out by risk), but they don't typically explain how the insurer arrived at that number.
