First, understand the specifications of a DVM.
The displays are usually specified as 3½ digit, 4½ digit or 4¾ digit, or something like that.
3½ digit means a maximum display of 1999
4½ digit means a maximum display of 19999
4¾ digit means a maximum display of 39999
So for a 3½ digit DVM reading 5 volts, the display may be 5.00, and for a 4½ digit DVM 5.000.
But if we now measure 500volts with the same DVMs
3½ digit 500
4½ digit 500.0
It is meaningless to think in terms of decimal places without thinking about the magnitude of the voltage.
This discussion just considers the RESOLUTION of the display, the ACCURACY is another thing entirely.
I am off to eat now, if we want to talk about accuracy, I will be back later.
JimB