I saw where 30 yr old meters are only bout 81% accurate, wouldnt the gallons b a factor also?
that depends on a number of factors.....
meter style....positive displacement (piston type), compound, Turbine, propeller or magnetic design.
using a standard 3/4 rockwell SR series piston meter as an example, it would not be uncommon for it to have 81% accuracy at 30 years old in the low 1/4 gpm to mid 2gpm range water flow range, depending on how bad the scoring (scratches) are in the measuring chamber. but it would not be surprising if its accuracy increases into the 90% range once you get above the 2gpm flow rate. 15GPM is the max test rate for this meter, i would not be surprised to see 15gpm also in the 90+% range
other brand meters such as Neptune and Badger 3/4 inch positive displacement meters do a better job measuring due to less surface area to drag in the chamber because they are nutating disk design instead of the piston design.
what i meant was i try to get u apicture of the prcission meter if i can figure out how to do it. and wouldnt the number of gallons on a meter have to do as much as the age as far as time to change it out?
in the 80s or 90s, Sensus bought out rockwells meter devision and continued the Piston meter design, until in the 90s they came out with the SRII series, its still a piston meter, but its designed a little different.
follow that link above to check out info ive posted about rockwell and sensus meters
if we are talking about smaller meters 5/8,3/4,1,1 1/2 meters the type i prefer are the Nutating disc type. for sizes above 1 1/2 inch i think the best design is a Compound. wich can accurately measure very small flows and large flows accurately.
i recently installed a 2 inch neptune TRU/FLO compound on a service that was previously seviced by a 2 inch Nutating disk meter. allthough the nutating disc did a good job at measuring general use, it doesnt quite read accurately below 1 GPM. the 2 inch TRU/FLO will measure to atleast 95% accuracy at 1/4 Gpm and will detect and record consumption of a steady dripping faucet leak.