I googled a few DDS844 references, and they all showed the numbers 5(20).
My GUESS is the 20 (30) is the current rating and maybe the 5 is the calibration value.
In Australia, there has been a huge love affair with electronic metering, and the electromechanical type has largely been superseded by the all electronic (remotely disconnectable, remotely read) types.
Electricity meters are required to be able to measure 60 amps per phase and I am certain the performance across the full load range would have to be guaranteed to better than 2% error under all conditions.