Here's a lesson (I can laugh about now that I'm retired): one of the first billing systems I ever wrote (in the 90's) had invoices with a mask of '$ZZ,ZZ9.99' b

Here's a lesson (I can laugh about now that I'm retired): one of the first billing systems I ever wrote (in the 90's) had invoices with a mask of '$ZZ,ZZ9.99' based on interviews with staff. About a year later I get an urgent call from the owner. It seems a client was under-billed about $100K dollars due to truncated invoice. Subsequently, whenever interviewing clients for requirements I'd mention this and it usually resulted in padding their specs.