I was wondering if anyone has any info as to the timekeeping error of a 7 jewel pocketwatch, lets say an 18 size Elgin from the late 1800s, when it was new.

The manufacturers must have had some sort of data on this.

On modern watches, this info is in the technical data sheets, but I would really like to find out what would have been acceptable for a watch back then.

Scott, Generally speaking the 7 Jewel movement using a temp compensated, cut, "vibrated" balance wheel and hairspring assembly should have been quite good when they were new as the real "error" occurs at the Balance wheel. That said, they were rarely expected to keep any better time than a few minutes a day and therefore would not have been as carefully studied, logged and compensated by the factory for temperature, position and isochronism.

A good watchmaker could probably fix the positional error, but temperature and isochronism required resources that were used before the watch was completely finished and cased.

I know this does not really answer your question, but the standards for these movements were probably on the order of a few minutes a week at best with deviations allowed for each day equalling the weekly drift due to temperature cycles.

Finally Elgin made some "Sun Dial" movements using uncut balance wheels that would guarantee five minutes or more daily time deviatins becaure ther could not be any chance of tmeperature compensation.