Down to experience - 1972, 2 years out of my apprenticeship and working in Production Enginnering, Salisbury Transmission (my employer) had just secured a prestigious order from the USA and initial machining trials were underway when my boss asked me to go and sort a problem out at the start of the gearbox manufacturing line. The tooling engineers had a mismatch between a milling machine and the cutter they were trying to fit to it, the solution: an adaptor, simple engineering solution, within an hour or so I had designed the part and it had been ordered and a few days later it came in, I shouldn't have heard anymore about it, but I did - foreman sent for saying you've messed up, adaptor fits the machine ok but the cutter wont marry up with the adaptor.
I checked my measurement and double checked the cutter - my meaurements were miles out and I couldn't understand it - there had to be a reason and of course there was - after much investigation I discovered a consultant engineer had been working on the machine and when the cutter couldn't be fitted it took it away for use elsewhere and the cutter they tried to fit later was not the same one although everyone swore blind it was.
I vowed I would never be caught out again and in simlar circustances I took a photograph of the items in question - now a days with a phone camera it would be easier.
Ah well! That's Life!
Peg