Format:
You will need to treat differently the whole part and the fraction part.
B4X:
Sub App_Start
Msgbox(SpecialFormat(1.2345678)) 'will display 001.235
End Sub
Sub SpecialFormat(num)
frac = Format(num - Int(num),"F3")
Return Format(Int(num),"d3") & SubString(frac,1,StrLength(frac)-1)
End Sub