There are restrictions of the DSP hardware.
WT230 and WT210 are low-cost power meters.
So, a low-cost, modest performance DSP utilized.
This DSP has slow calculation.
WT3000 is performing complicated calculation in order to maintain high accuracy.
So WT3000's DSP needs a long time to calculate the data.
If a lot of data is calculated simultaneously, it will not be in time for the update time of measurement.
There was only one way to calculate only one mode Urms, Umn or Udc.
So, WT210, WT230 and WT3000 can not calculate Urms, Unm, and Udc simultaneously.
PZ4000, WT1600, WT1800 and WT500 have a high speed DSP.
So they can calculate Urms, Unm, and Udc simultaneously.