Engineering and quant staff inside financial institutions need to produce and maintain internal models and reporting tools for derivatives pricing, hedging and compliance calculations.
By industry convention such internal tools are usually hand-written by the institution's own engineers or bought from established financial software vendors; the candidate material does not confirm the prior practice.
The candidate material is only a headline; it does not say which step was most time-consuming or how costly errors were, so the pain cannot be reconstructed from public facts.