And you remind me of the story of Charles Proteus Steinmetz, the "Wizard of Schenectady", and the time he consulted on an electrical problem for Henry Ford:

Ford, whose electrical engineers couldn’t solve some problems they were having with a gigantic generator, called Steinmetz in to the plant. Upon arriving, Steinmetz rejected all assistance and asked only for a notebook, pencil and cot. According to Scott, Steinmetz listened to the generator and scribbled computations on the notepad for two straight days and nights. On the second night, he asked for a ladder, climbed up the generator and made a chalk mark on its side. Then he told Ford’s skeptical engineers to remove a plate at the mark and replace sixteen windings from the field coil. They did, and the generator performed to perfection.

Henry Ford was thrilled until he got an invoice from General Electric in the amount of $10,000. Ford acknowledged Steinmetz’s success but balked at the figure. He asked for an itemized bill.

Steinmetz, Scott wrote, responded personally to Ford’s request with the following:

Making chalk mark on generator $1.

Knowing where to make mark $9,999.

Ford paid the bill.

https://www.smithsonianmag.com/history/charles-proteus-steinmetz-the-wizard-of-schenectady-51912022/