[D9248AAL], Letter from Thomas Alva Edison to John F Ott, October 24th, 1892
https://edisondigital.rutgers.edu/document/D9248AAL
Transcription
[TO JOHN OTT?] If with volts marked the Lamps last 1000 [illegible text] hours then 3 volts high only last 700 400 125 now before you make a complaint get a record several times each nights of your volts where Lamps are then if it don’t come outright you can call for investigation, in nearly every instance where parties make complaint their volts were found on investigation too high you should have a breakage of 4 or 5 a day <Oct 24th 1892>