Multiply by 1 and add the option decimals=1
Example:
Set V[d2] "58.21" Set V[d1] "&V[d2]" * 1 decimals=1 // now V[d1] is "58.2"
The value is rounded automatically. Example:
Set V[d2] "58.27" Set V[d1] "&V[d2]" * 1 decimals=1 // now V[d1] is "58.3"