It's a little hard to put an exact age on this meter. The serial number predates the convention that was adopted in 1981, so we know that it is at least 35 years old.
The meter is back at Max for a calibration. The last time that this meter was here was in 1996. Since it lacks a linearizing transmitter, we had to calibrate against its original specification. Here is the data from our only other calibration, 20 years ago.
Here is the data from today.
Pretty incredible. The meter has not been serviced for 20 years and the K-Factors have hardly drifted.
We can't promise that every well cared for meter will work for 20 years between calibrations. So, we'd suggest a shorter interval between calibrations to ensure that your meters are still providing reliable performance.