Rod
With a maximum variance of only 0.3V from your DMM, your circuit is accurate enough for its intended use: monitoring track voltage. I'm running command using Z-1000 and PH-180 bricks, and a Z-4000, (all sine wave) so this should work for me. Here is a list of sine wave train transformers. Mike Regan did a detailed video of chopped vs sine wave transformers here.
Bob
Sine wave Transformers:
All Lionel and AF post war transformers
Lionel Powerhouse 135 and 180
MTH Z-1000, Z-750, and Z-500 (brick only - no controller)
MTH Z-4000
MRC Pure Power AC
Right of Way 2020